diff --git a/py/bc.h b/py/bc.h
index 35847f4..6a7b916 100644
--- a/py/bc.h
+++ b/py/bc.h
@@ -1,2 +1,2 @@
 mp_obj_t mp_execute_byte_code(const byte *code, const mp_obj_t *args, uint n_args, uint n_state);
-bool mp_execute_byte_code_2(const byte **ip_in_out, mp_obj_t *fastn, mp_obj_t **sp_in_out);
+bool mp_execute_byte_code_2(const byte *code_info, const byte **ip_in_out, mp_obj_t *fastn, mp_obj_t **sp_in_out);
diff --git a/py/builtineval.c b/py/builtineval.c
index a8a7a47..c7bd6b6 100644
--- a/py/builtineval.c
+++ b/py/builtineval.c
@@ -28,6 +28,7 @@
     qstr parse_exc_id;
     const char *parse_exc_msg;
     mp_parse_node_t pn = mp_parse(lex, MP_PARSE_EVAL_INPUT, &parse_exc_id, &parse_exc_msg);
+    qstr source_name = mp_lexer_source_name(lex);
     mp_lexer_free(lex);
 
     if (pn == MP_PARSE_NODE_NULL) {
@@ -36,7 +37,7 @@
     }
 
     // compile the string
-    mp_obj_t module_fun = mp_compile(pn, false);
+    mp_obj_t module_fun = mp_compile(pn, source_name, false);
 
     if (module_fun == mp_const_none) {
         // TODO handle compile error correctly
diff --git a/py/builtinimport.c b/py/builtinimport.c
index 2eca36f..e3c630a 100644
--- a/py/builtinimport.c
+++ b/py/builtinimport.c
@@ -51,6 +51,7 @@
     qstr parse_exc_id;
     const char *parse_exc_msg;
     mp_parse_node_t pn = mp_parse(lex, MP_PARSE_FILE_INPUT, &parse_exc_id, &parse_exc_msg);
+    qstr source_name = mp_lexer_source_name(lex);
     mp_lexer_free(lex);
 
     if (pn == MP_PARSE_NODE_NULL) {
@@ -61,7 +62,7 @@
     }
 
     // compile the imported script
-    mp_obj_t module_fun = mp_compile(pn, false);
+    mp_obj_t module_fun = mp_compile(pn, source_name, false);
 
     if (module_fun == mp_const_none) {
         // TODO handle compile error correctly
diff --git a/py/compile.c b/py/compile.c
index b24e94a..cf87e01 100644
--- a/py/compile.c
+++ b/py/compile.c
@@ -2505,6 +2505,7 @@
         }
     } else {
         mp_parse_node_struct_t *pns = (mp_parse_node_struct_t*)pn;
+        EMIT(set_line_number, pns->source_line);
         compile_function_t f = compile_function[MP_PARSE_NODE_STRUCT_KIND(pns)];
         if (f == NULL) {
             printf("node %u cannot be compiled\n", (uint)MP_PARSE_NODE_STRUCT_KIND(pns));
@@ -3024,7 +3025,7 @@
     }
 }
 
-mp_obj_t mp_compile(mp_parse_node_t pn, bool is_repl) {
+mp_obj_t mp_compile(mp_parse_node_t pn, qstr source_file, bool is_repl) {
     compiler_t *comp = m_new(compiler_t, 1);
 
     comp->is_repl = is_repl;
@@ -3131,7 +3132,7 @@
 
                 default:
                     if (emit_bc == NULL) {
-                        emit_bc = emit_bc_new(max_num_labels);
+                        emit_bc = emit_bc_new(source_file, max_num_labels);
                     }
                     comp->emit = emit_bc;
                     comp->emit_method_table = &emit_bc_method_table;
diff --git a/py/compile.h b/py/compile.h
index 770c252..552d36f 100644
--- a/py/compile.h
+++ b/py/compile.h
@@ -1 +1 @@
-mp_obj_t mp_compile(mp_parse_node_t pn, bool is_repl);
+mp_obj_t mp_compile(mp_parse_node_t pn, qstr source_file, bool is_repl);
diff --git a/py/emit.h b/py/emit.h
index fd41764..521b43c 100644
--- a/py/emit.h
+++ b/py/emit.h
@@ -23,6 +23,7 @@
     bool (*last_emit_was_return_value)(emit_t *emit);
     int (*get_stack_size)(emit_t *emit);
     void (*set_stack_size)(emit_t *emit, int size);
+    void (*set_line_number)(emit_t *emit, int line);
 
     void (*load_id)(emit_t *emit, qstr qstr);
     void (*store_id)(emit_t *emit, qstr qstr);
@@ -119,7 +120,7 @@
 emit_t *emit_pass1_new(qstr qstr___class__);
 void emit_pass1_free(emit_t *emit);
 emit_t *emit_cpython_new(uint max_num_labels);
-emit_t *emit_bc_new(uint max_num_labels);
+emit_t *emit_bc_new(qstr source_file, uint max_num_labels);
 emit_t *emit_native_x64_new(uint max_num_labels);
 emit_t *emit_native_thumb_new(uint max_num_labels);
 
diff --git a/py/emitbc.c b/py/emitbc.c
index fdef070..e1a81ad 100644
--- a/py/emitbc.c
+++ b/py/emitbc.c
@@ -21,79 +21,104 @@
 
     scope_t *scope;
 
+    qstr source_file;
+    uint last_source_line_offset;
+    uint last_source_line;
+
     uint max_num_labels;
     uint *label_offsets;
 
-    uint code_offset;
-    uint code_size;
-    byte *code_base;
+    uint code_info_offset;
+    uint code_info_size;
+    uint byte_code_offset;
+    uint byte_code_size;
+    byte *code_base; // stores both byte code and code info
     byte dummy_data[8];
 };
 
-emit_t *emit_bc_new(uint max_num_labels) {
-    emit_t *emit = m_new(emit_t, 1);
+emit_t *emit_bc_new(qstr source_file, uint max_num_labels) {
+    emit_t *emit = m_new0(emit_t, 1);
+    emit->source_file = source_file;
     emit->max_num_labels = max_num_labels;
     emit->label_offsets = m_new(uint, emit->max_num_labels);
-    emit->code_offset = 0;
-    emit->code_size = 0;
-    emit->code_base = NULL;
     return emit;
 }
 
-uint emit_bc_get_code_size(emit_t* emit) {
-    return emit->code_size;
-}
-
-void* emit_bc_get_code(emit_t* emit) {
-    return emit->code_base;
-}
-
-// all functions must go through this one to emit bytes
-static byte* emit_get_cur_to_write_bytes(emit_t* emit, int num_bytes_to_write) {
+// all functions must go through this one to emit code info
+static byte* emit_get_cur_to_write_code_info(emit_t* emit, int num_bytes_to_write) {
     //printf("emit %d\n", num_bytes_to_write);
     if (emit->pass < PASS_3) {
-        emit->code_offset += num_bytes_to_write;
+        emit->code_info_offset += num_bytes_to_write;
         return emit->dummy_data;
     } else {
-        assert(emit->code_offset + num_bytes_to_write <= emit->code_size);
-        byte *c = emit->code_base + emit->code_offset;
-        emit->code_offset += num_bytes_to_write;
+        assert(emit->code_info_offset + num_bytes_to_write <= emit->code_info_size);
+        byte *c = emit->code_base + emit->code_info_offset;
+        emit->code_info_offset += num_bytes_to_write;
         return c;
     }
 }
 
-static void emit_write_byte_1(emit_t* emit, byte b1) {
-    byte* c = emit_get_cur_to_write_bytes(emit, 1);
+static void emit_write_code_info_qstr(emit_t* emit, qstr qstr) {
+    byte* c = emit_get_cur_to_write_code_info(emit, 4);
+    // TODO variable length encoding for qstr
+    c[0] = qstr & 0xff;
+    c[1] = (qstr >> 8) & 0xff;
+    c[2] = (qstr >> 16) & 0xff;
+    c[3] = (qstr >> 24) & 0xff;
+}
+
+static void emit_write_code_info_byte_byte(emit_t* emit, byte b1, uint b2) {
+    byte* c = emit_get_cur_to_write_code_info(emit, 2);
+    c[0] = b1;
+    c[1] = b2;
+}
+
+// all functions must go through this one to emit byte code
+static byte* emit_get_cur_to_write_byte_code(emit_t* emit, int num_bytes_to_write) {
+    //printf("emit %d\n", num_bytes_to_write);
+    if (emit->pass < PASS_3) {
+        emit->byte_code_offset += num_bytes_to_write;
+        return emit->dummy_data;
+    } else {
+        assert(emit->byte_code_offset + num_bytes_to_write <= emit->byte_code_size);
+        byte *c = emit->code_base + emit->code_info_size + emit->byte_code_offset;
+        emit->byte_code_offset += num_bytes_to_write;
+        return c;
+    }
+}
+
+static void emit_write_byte_code_byte(emit_t* emit, byte b1) {
+    byte* c = emit_get_cur_to_write_byte_code(emit, 1);
     c[0] = b1;
 }
 
-static void emit_write_byte_1_byte(emit_t* emit, byte b1, uint b2) {
+static void emit_write_byte_code_byte_byte(emit_t* emit, byte b1, uint b2) {
     assert((b2 & (~0xff)) == 0);
-    byte* c = emit_get_cur_to_write_bytes(emit, 2);
+    byte* c = emit_get_cur_to_write_byte_code(emit, 2);
     c[0] = b1;
     c[1] = b2;
 }
 
 // integers (for small ints) are stored as 24 bits, in excess
-static void emit_write_byte_1_int(emit_t* emit, byte b1, int num) {
+static void emit_write_byte_code_byte_int(emit_t* emit, byte b1, int num) {
     num += 0x800000;
     assert(0 <= num && num <= 0xffffff);
-    byte* c = emit_get_cur_to_write_bytes(emit, 4);
+    byte* c = emit_get_cur_to_write_byte_code(emit, 4);
     c[0] = b1;
     c[1] = num;
     c[2] = num >> 8;
     c[3] = num >> 16;
 }
 
-static void emit_write_byte_1_uint(emit_t* emit, byte b1, uint num) {
+static void emit_write_byte_code_byte_uint(emit_t* emit, byte b1, uint num) {
     if (num <= 127) { // fits in 0x7f
         // fit argument in single byte
-        byte* c = emit_get_cur_to_write_bytes(emit, 2);
+        byte* c = emit_get_cur_to_write_byte_code(emit, 2);
         c[0] = b1;
         c[1] = num;
     } else if (num <= 16383) { // fits in 0x3fff
         // fit argument in two bytes
-        byte* c = emit_get_cur_to_write_bytes(emit, 3);
+        byte* c = emit_get_cur_to_write_byte_code(emit, 3);
         c[0] = b1;
         c[1] = (num >> 8) | 0x80;
         c[2] = num;
@@ -103,36 +128,36 @@
     }
 }
 
-static void emit_write_byte_1_qstr(emit_t* emit, byte b1, qstr qstr) {
-    emit_write_byte_1_uint(emit, b1, qstr);
+static void emit_write_byte_code_byte_qstr(emit_t* emit, byte b1, qstr qstr) {
+    emit_write_byte_code_byte_uint(emit, b1, qstr);
 }
 
 // unsigned labels are relative to ip following this instruction, stored as 16 bits
-static void emit_write_byte_1_unsigned_label(emit_t* emit, byte b1, int label) {
-    uint code_offset;
+static void emit_write_byte_code_byte_unsigned_label(emit_t* emit, byte b1, int label) {
+    uint byte_code_offset;
     if (emit->pass < PASS_3) {
-        code_offset = 0;
+        byte_code_offset = 0;
     } else {
-        code_offset = emit->label_offsets[label] - emit->code_offset - 3;
+        byte_code_offset = emit->label_offsets[label] - emit->byte_code_offset - 3;
     }
-    byte* c = emit_get_cur_to_write_bytes(emit, 3);
+    byte* c = emit_get_cur_to_write_byte_code(emit, 3);
     c[0] = b1;
-    c[1] = code_offset;
-    c[2] = code_offset >> 8;
+    c[1] = byte_code_offset;
+    c[2] = byte_code_offset >> 8;
 }
 
 // signed labels are relative to ip following this instruction, stored as 16 bits, in excess
-static void emit_write_byte_1_signed_label(emit_t* emit, byte b1, int label) {
-    int code_offset;
+static void emit_write_byte_code_byte_signed_label(emit_t* emit, byte b1, int label) {
+    int byte_code_offset;
     if (emit->pass < PASS_3) {
-        code_offset = 0;
+        byte_code_offset = 0;
     } else {
-        code_offset = emit->label_offsets[label] - emit->code_offset - 3 + 0x8000;
+        byte_code_offset = emit->label_offsets[label] - emit->byte_code_offset - 3 + 0x8000;
     }
-    byte* c = emit_get_cur_to_write_bytes(emit, 3);
+    byte* c = emit_get_cur_to_write_byte_code(emit, 3);
     c[0] = b1;
-    c[1] = code_offset;
-    c[2] = code_offset >> 8;
+    c[1] = byte_code_offset;
+    c[2] = byte_code_offset >> 8;
 }
 
 static void emit_bc_set_native_types(emit_t *emit, bool do_native_types) {
@@ -143,10 +168,26 @@
     emit->stack_size = 0;
     emit->last_emit_was_return_value = false;
     emit->scope = scope;
+    emit->last_source_line_offset = 0;
+    emit->last_source_line = 1;
     if (pass == PASS_2) {
         memset(emit->label_offsets, -1, emit->max_num_labels * sizeof(uint));
     }
-    emit->code_offset = 0;
+    emit->byte_code_offset = 0;
+    emit->code_info_offset = 0;
+
+    // write code info size (don't know size at this stage in PASS_2 so need to use maximum space (4 bytes) to write it)
+    {
+        byte* c = emit_get_cur_to_write_code_info(emit, 4);
+        machine_uint_t s = emit->code_info_size;
+        c[0] = s & 0xff;
+        c[1] = (s >> 8) & 0xff;
+        c[2] = (s >> 16) & 0xff;
+        c[3] = (s >> 24) & 0xff;
+    }
+
+    // code info
+    emit_write_code_info_qstr(emit, emit->source_file);
 
     // prelude for initialising closed over variables
     int num_cell = 0;
@@ -157,11 +198,11 @@
         }
     }
     assert(num_cell <= 255);
-    emit_write_byte_1(emit, num_cell); // write number of locals that are cells
+    emit_write_byte_code_byte(emit, num_cell); // write number of locals that are cells
     for (int i = 0; i < scope->id_info_len; i++) {
         id_info_t *id = &scope->id_info[i];
         if (id->kind == ID_INFO_KIND_CELL) {
-            emit_write_byte_1(emit, id->local_num); // write the local which should be converted to a cell
+            emit_write_byte_code_byte(emit, id->local_num); // write the local which should be converted to a cell
         }
     }
 }
@@ -172,13 +213,16 @@
         printf("ERROR: stack size not back to zero; got %d\n", emit->stack_size);
     }
 
+    emit_write_code_info_byte_byte(emit, 0, 0); // end of line number info
+
     if (emit->pass == PASS_2) {
         // calculate size of code in bytes
-        emit->code_size = emit->code_offset;
-        emit->code_base = m_new(byte, emit->code_size);
+        emit->code_info_size = emit->code_info_offset;
+        emit->byte_code_size = emit->byte_code_offset;
+        emit->code_base = m_new(byte, emit->code_info_size + emit->byte_code_size);
 
     } else if (emit->pass == PASS_3) {
-        rt_assign_byte_code(emit->scope->unique_code_id, emit->code_base, emit->code_size, emit->scope->num_params, emit->scope->num_locals, emit->scope->stack_size, (emit->scope->flags & SCOPE_FLAG_GENERATOR) != 0);
+        rt_assign_byte_code(emit->scope->unique_code_id, emit->code_base, emit->code_info_size + emit->byte_code_size, emit->scope->num_params, emit->scope->num_locals, emit->scope->stack_size, (emit->scope->flags & SCOPE_FLAG_GENERATOR) != 0);
     }
 }
 
@@ -194,6 +238,22 @@
     emit->stack_size = size;
 }
 
+static void emit_bc_set_source_line(emit_t *emit, int source_line) {
+    if (source_line > emit->last_source_line) {
+        int bytes_to_skip = emit->byte_code_offset - emit->last_source_line_offset;
+        for (; bytes_to_skip > 255; bytes_to_skip -= 255) {
+            emit_write_code_info_byte_byte(emit, 255, 0);
+        }
+        int lines_to_skip = source_line - emit->last_source_line;
+        for (; lines_to_skip > 255; lines_to_skip -= 255) {
+            emit_write_code_info_byte_byte(emit, 0, 255);
+        }
+        emit_write_code_info_byte_byte(emit, bytes_to_skip, lines_to_skip);
+        emit->last_source_line_offset = emit->byte_code_offset;
+        emit->last_source_line = source_line;
+    }
+}
+
 static void emit_bc_load_id(emit_t *emit, qstr qstr) {
     emit_common_load_id(emit, &emit_bc_method_table, emit->scope, qstr);
 }
@@ -220,66 +280,66 @@
     if (emit->pass == PASS_2) {
         // assign label offset
         assert(emit->label_offsets[l] == -1);
-        emit->label_offsets[l] = emit->code_offset;
+        emit->label_offsets[l] = emit->byte_code_offset;
     } else if (emit->pass == PASS_3) {
         // ensure label offset has not changed from PASS_2 to PASS_3
-        //printf("l%d: (at %d vs %d)\n", l, emit->code_offset, emit->label_offsets[l]);
-        assert(emit->label_offsets[l] == emit->code_offset);
+        //printf("l%d: (at %d vs %d)\n", l, emit->byte_code_offset, emit->label_offsets[l]);
+        assert(emit->label_offsets[l] == emit->byte_code_offset);
     }
 }
 
 static void emit_bc_import_name(emit_t *emit, qstr qstr) {
     emit_pre(emit, -1);
-    emit_write_byte_1_qstr(emit, MP_BC_IMPORT_NAME, qstr);
+    emit_write_byte_code_byte_qstr(emit, MP_BC_IMPORT_NAME, qstr);
 }
 
 static void emit_bc_import_from(emit_t *emit, qstr qstr) {
     emit_pre(emit, 1);
-    emit_write_byte_1_qstr(emit, MP_BC_IMPORT_FROM, qstr);
+    emit_write_byte_code_byte_qstr(emit, MP_BC_IMPORT_FROM, qstr);
 }
 
 static void emit_bc_import_star(emit_t *emit) {
     emit_pre(emit, -1);
-    emit_write_byte_1(emit, MP_BC_IMPORT_STAR);
+    emit_write_byte_code_byte(emit, MP_BC_IMPORT_STAR);
 }
 
 static void emit_bc_load_const_tok(emit_t *emit, mp_token_kind_t tok) {
     emit_pre(emit, 1);
     switch (tok) {
-        case MP_TOKEN_KW_FALSE: emit_write_byte_1(emit, MP_BC_LOAD_CONST_FALSE); break;
-        case MP_TOKEN_KW_NONE: emit_write_byte_1(emit, MP_BC_LOAD_CONST_NONE); break;
-        case MP_TOKEN_KW_TRUE: emit_write_byte_1(emit, MP_BC_LOAD_CONST_TRUE); break;
-        case MP_TOKEN_ELLIPSIS: emit_write_byte_1(emit, MP_BC_LOAD_CONST_ELLIPSIS); break;
+        case MP_TOKEN_KW_FALSE: emit_write_byte_code_byte(emit, MP_BC_LOAD_CONST_FALSE); break;
+        case MP_TOKEN_KW_NONE: emit_write_byte_code_byte(emit, MP_BC_LOAD_CONST_NONE); break;
+        case MP_TOKEN_KW_TRUE: emit_write_byte_code_byte(emit, MP_BC_LOAD_CONST_TRUE); break;
+        case MP_TOKEN_ELLIPSIS: emit_write_byte_code_byte(emit, MP_BC_LOAD_CONST_ELLIPSIS); break;
         default: assert(0);
     }
 }
 
 static void emit_bc_load_const_small_int(emit_t *emit, int arg) {
     emit_pre(emit, 1);
-    emit_write_byte_1_int(emit, MP_BC_LOAD_CONST_SMALL_INT, arg);
+    emit_write_byte_code_byte_int(emit, MP_BC_LOAD_CONST_SMALL_INT, arg);
 }
 
 static void emit_bc_load_const_int(emit_t *emit, qstr qstr) {
     emit_pre(emit, 1);
-    emit_write_byte_1_qstr(emit, MP_BC_LOAD_CONST_INT, qstr);
+    emit_write_byte_code_byte_qstr(emit, MP_BC_LOAD_CONST_INT, qstr);
 }
 
 static void emit_bc_load_const_dec(emit_t *emit, qstr qstr) {
     emit_pre(emit, 1);
-    emit_write_byte_1_qstr(emit, MP_BC_LOAD_CONST_DEC, qstr);
+    emit_write_byte_code_byte_qstr(emit, MP_BC_LOAD_CONST_DEC, qstr);
 }
 
 static void emit_bc_load_const_id(emit_t *emit, qstr qstr) {
     emit_pre(emit, 1);
-    emit_write_byte_1_qstr(emit, MP_BC_LOAD_CONST_ID, qstr);
+    emit_write_byte_code_byte_qstr(emit, MP_BC_LOAD_CONST_ID, qstr);
 }
 
 static void emit_bc_load_const_str(emit_t *emit, qstr qstr, bool bytes) {
     emit_pre(emit, 1);
     if (bytes) {
-        emit_write_byte_1_qstr(emit, MP_BC_LOAD_CONST_BYTES, qstr);
+        emit_write_byte_code_byte_qstr(emit, MP_BC_LOAD_CONST_BYTES, qstr);
     } else {
-        emit_write_byte_1_qstr(emit, MP_BC_LOAD_CONST_STRING, qstr);
+        emit_write_byte_code_byte_qstr(emit, MP_BC_LOAD_CONST_STRING, qstr);
     }
 }
 
@@ -292,16 +352,16 @@
     assert(local_num >= 0);
     emit_pre(emit, 1);
     switch (local_num) {
-        case 0: emit_write_byte_1(emit, MP_BC_LOAD_FAST_0); break;
-        case 1: emit_write_byte_1(emit, MP_BC_LOAD_FAST_1); break;
-        case 2: emit_write_byte_1(emit, MP_BC_LOAD_FAST_2); break;
-        default: emit_write_byte_1_uint(emit, MP_BC_LOAD_FAST_N, local_num); break;
+        case 0: emit_write_byte_code_byte(emit, MP_BC_LOAD_FAST_0); break;
+        case 1: emit_write_byte_code_byte(emit, MP_BC_LOAD_FAST_1); break;
+        case 2: emit_write_byte_code_byte(emit, MP_BC_LOAD_FAST_2); break;
+        default: emit_write_byte_code_byte_uint(emit, MP_BC_LOAD_FAST_N, local_num); break;
     }
 }
 
 static void emit_bc_load_deref(emit_t *emit, qstr qstr, int local_num) {
     emit_pre(emit, 1);
-    emit_write_byte_1_uint(emit, MP_BC_LOAD_DEREF, local_num);
+    emit_write_byte_code_byte_uint(emit, MP_BC_LOAD_DEREF, local_num);
 }
 
 static void emit_bc_load_closure(emit_t *emit, qstr qstr, int local_num) {
@@ -311,200 +371,200 @@
 
 static void emit_bc_load_name(emit_t *emit, qstr qstr) {
     emit_pre(emit, 1);
-    emit_write_byte_1_qstr(emit, MP_BC_LOAD_NAME, qstr);
+    emit_write_byte_code_byte_qstr(emit, MP_BC_LOAD_NAME, qstr);
 }
 
 static void emit_bc_load_global(emit_t *emit, qstr qstr) {
     emit_pre(emit, 1);
-    emit_write_byte_1_qstr(emit, MP_BC_LOAD_GLOBAL, qstr);
+    emit_write_byte_code_byte_qstr(emit, MP_BC_LOAD_GLOBAL, qstr);
 }
 
 static void emit_bc_load_attr(emit_t *emit, qstr qstr) {
     emit_pre(emit, 0);
-    emit_write_byte_1_qstr(emit, MP_BC_LOAD_ATTR, qstr);
+    emit_write_byte_code_byte_qstr(emit, MP_BC_LOAD_ATTR, qstr);
 }
 
 static void emit_bc_load_method(emit_t *emit, qstr qstr) {
     emit_pre(emit, 0);
-    emit_write_byte_1_qstr(emit, MP_BC_LOAD_METHOD, qstr);
+    emit_write_byte_code_byte_qstr(emit, MP_BC_LOAD_METHOD, qstr);
 }
 
 static void emit_bc_load_build_class(emit_t *emit) {
     emit_pre(emit, 1);
-    emit_write_byte_1(emit, MP_BC_LOAD_BUILD_CLASS);
+    emit_write_byte_code_byte(emit, MP_BC_LOAD_BUILD_CLASS);
 }
 
 static void emit_bc_store_fast(emit_t *emit, qstr qstr, int local_num) {
     assert(local_num >= 0);
     emit_pre(emit, -1);
     switch (local_num) {
-        case 0: emit_write_byte_1(emit, MP_BC_STORE_FAST_0); break;
-        case 1: emit_write_byte_1(emit, MP_BC_STORE_FAST_1); break;
-        case 2: emit_write_byte_1(emit, MP_BC_STORE_FAST_2); break;
-        default: emit_write_byte_1_uint(emit, MP_BC_STORE_FAST_N, local_num); break;
+        case 0: emit_write_byte_code_byte(emit, MP_BC_STORE_FAST_0); break;
+        case 1: emit_write_byte_code_byte(emit, MP_BC_STORE_FAST_1); break;
+        case 2: emit_write_byte_code_byte(emit, MP_BC_STORE_FAST_2); break;
+        default: emit_write_byte_code_byte_uint(emit, MP_BC_STORE_FAST_N, local_num); break;
     }
 }
 
 static void emit_bc_store_deref(emit_t *emit, qstr qstr, int local_num) {
     emit_pre(emit, -1);
-    emit_write_byte_1_uint(emit, MP_BC_STORE_DEREF, local_num);
+    emit_write_byte_code_byte_uint(emit, MP_BC_STORE_DEREF, local_num);
 }
 
 static void emit_bc_store_name(emit_t *emit, qstr qstr) {
     emit_pre(emit, -1);
-    emit_write_byte_1_qstr(emit, MP_BC_STORE_NAME, qstr);
+    emit_write_byte_code_byte_qstr(emit, MP_BC_STORE_NAME, qstr);
 }
 
 static void emit_bc_store_global(emit_t *emit, qstr qstr) {
     emit_pre(emit, -1);
-    emit_write_byte_1_qstr(emit, MP_BC_STORE_GLOBAL, qstr);
+    emit_write_byte_code_byte_qstr(emit, MP_BC_STORE_GLOBAL, qstr);
 }
 
 static void emit_bc_store_attr(emit_t *emit, qstr qstr) {
     emit_pre(emit, -2);
-    emit_write_byte_1_qstr(emit, MP_BC_STORE_ATTR, qstr);
+    emit_write_byte_code_byte_qstr(emit, MP_BC_STORE_ATTR, qstr);
 }
 
 static void emit_bc_store_subscr(emit_t *emit) {
     emit_pre(emit, -3);
-    emit_write_byte_1(emit, MP_BC_STORE_SUBSCR);
+    emit_write_byte_code_byte(emit, MP_BC_STORE_SUBSCR);
 }
 
 static void emit_bc_store_locals(emit_t *emit) {
     // not needed
     emit_pre(emit, -1);
-    emit_write_byte_1(emit, MP_BC_POP_TOP);
+    emit_write_byte_code_byte(emit, MP_BC_POP_TOP);
 }
 
 static void emit_bc_delete_fast(emit_t *emit, qstr qstr, int local_num) {
     assert(local_num >= 0);
     emit_pre(emit, 0);
-    emit_write_byte_1_uint(emit, MP_BC_DELETE_FAST_N, local_num);
+    emit_write_byte_code_byte_uint(emit, MP_BC_DELETE_FAST_N, local_num);
 }
 
 static void emit_bc_delete_deref(emit_t *emit, qstr qstr, int local_num) {
     emit_pre(emit, 0);
-    emit_write_byte_1_qstr(emit, MP_BC_DELETE_DEREF, local_num);
+    emit_write_byte_code_byte_qstr(emit, MP_BC_DELETE_DEREF, local_num);
 }
 
 static void emit_bc_delete_name(emit_t *emit, qstr qstr) {
     emit_pre(emit, 0);
-    emit_write_byte_1_qstr(emit, MP_BC_DELETE_NAME, qstr);
+    emit_write_byte_code_byte_qstr(emit, MP_BC_DELETE_NAME, qstr);
 }
 
 static void emit_bc_delete_global(emit_t *emit, qstr qstr) {
     emit_pre(emit, 0);
-    emit_write_byte_1_qstr(emit, MP_BC_DELETE_GLOBAL, qstr);
+    emit_write_byte_code_byte_qstr(emit, MP_BC_DELETE_GLOBAL, qstr);
 }
 
 static void emit_bc_delete_attr(emit_t *emit, qstr qstr) {
     emit_pre(emit, -1);
-    emit_write_byte_1_qstr(emit, MP_BC_DELETE_ATTR, qstr);
+    emit_write_byte_code_byte_qstr(emit, MP_BC_DELETE_ATTR, qstr);
 }
 
 static void emit_bc_delete_subscr(emit_t *emit) {
     emit_pre(emit, -2);
-    emit_write_byte_1(emit, MP_BC_DELETE_SUBSCR);
+    emit_write_byte_code_byte(emit, MP_BC_DELETE_SUBSCR);
 }
 
 static void emit_bc_dup_top(emit_t *emit) {
     emit_pre(emit, 1);
-    emit_write_byte_1(emit, MP_BC_DUP_TOP);
+    emit_write_byte_code_byte(emit, MP_BC_DUP_TOP);
 }
 
 static void emit_bc_dup_top_two(emit_t *emit) {
     emit_pre(emit, 2);
-    emit_write_byte_1(emit, MP_BC_DUP_TOP_TWO);
+    emit_write_byte_code_byte(emit, MP_BC_DUP_TOP_TWO);
 }
 
 static void emit_bc_pop_top(emit_t *emit) {
     emit_pre(emit, -1);
-    emit_write_byte_1(emit, MP_BC_POP_TOP);
+    emit_write_byte_code_byte(emit, MP_BC_POP_TOP);
 }
 
 static void emit_bc_rot_two(emit_t *emit) {
     emit_pre(emit, 0);
-    emit_write_byte_1(emit, MP_BC_ROT_TWO);
+    emit_write_byte_code_byte(emit, MP_BC_ROT_TWO);
 }
 
 static void emit_bc_rot_three(emit_t *emit) {
     emit_pre(emit, 0);
-    emit_write_byte_1(emit, MP_BC_ROT_THREE);
+    emit_write_byte_code_byte(emit, MP_BC_ROT_THREE);
 }
 
 static void emit_bc_jump(emit_t *emit, int label) {
     emit_pre(emit, 0);
-    emit_write_byte_1_signed_label(emit, MP_BC_JUMP, label);
+    emit_write_byte_code_byte_signed_label(emit, MP_BC_JUMP, label);
 }
 
 static void emit_bc_pop_jump_if_true(emit_t *emit, int label) {
     emit_pre(emit, -1);
-    emit_write_byte_1_signed_label(emit, MP_BC_POP_JUMP_IF_TRUE, label);
+    emit_write_byte_code_byte_signed_label(emit, MP_BC_POP_JUMP_IF_TRUE, label);
 }
 
 static void emit_bc_pop_jump_if_false(emit_t *emit, int label) {
     emit_pre(emit, -1);
-    emit_write_byte_1_signed_label(emit, MP_BC_POP_JUMP_IF_FALSE, label);
+    emit_write_byte_code_byte_signed_label(emit, MP_BC_POP_JUMP_IF_FALSE, label);
 }
 
 static void emit_bc_jump_if_true_or_pop(emit_t *emit, int label) {
     emit_pre(emit, -1);
-    emit_write_byte_1_signed_label(emit, MP_BC_JUMP_IF_TRUE_OR_POP, label);
+    emit_write_byte_code_byte_signed_label(emit, MP_BC_JUMP_IF_TRUE_OR_POP, label);
 }
 
 static void emit_bc_jump_if_false_or_pop(emit_t *emit, int label) {
     emit_pre(emit, -1);
-    emit_write_byte_1_signed_label(emit, MP_BC_JUMP_IF_FALSE_OR_POP, label);
+    emit_write_byte_code_byte_signed_label(emit, MP_BC_JUMP_IF_FALSE_OR_POP, label);
 }
 
 static void emit_bc_setup_loop(emit_t *emit, int label) {
     emit_pre(emit, 0);
-    emit_write_byte_1_unsigned_label(emit, MP_BC_SETUP_LOOP, label);
+    emit_write_byte_code_byte_unsigned_label(emit, MP_BC_SETUP_LOOP, label);
 }
 
 static void emit_bc_break_loop(emit_t *emit, int label) {
     emit_pre(emit, 0);
-    emit_write_byte_1_unsigned_label(emit, MP_BC_BREAK_LOOP, label);
+    emit_write_byte_code_byte_unsigned_label(emit, MP_BC_BREAK_LOOP, label);
 }
 
 static void emit_bc_continue_loop(emit_t *emit, int label) {
     emit_pre(emit, 0);
-    emit_write_byte_1_unsigned_label(emit, MP_BC_CONTINUE_LOOP, label);
+    emit_write_byte_code_byte_unsigned_label(emit, MP_BC_CONTINUE_LOOP, label);
 }
 
 static void emit_bc_setup_with(emit_t *emit, int label) {
     emit_pre(emit, 7);
-    emit_write_byte_1_unsigned_label(emit, MP_BC_SETUP_WITH, label);
+    emit_write_byte_code_byte_unsigned_label(emit, MP_BC_SETUP_WITH, label);
 }
 
 static void emit_bc_with_cleanup(emit_t *emit) {
     emit_pre(emit, -7);
-    emit_write_byte_1(emit, MP_BC_WITH_CLEANUP);
+    emit_write_byte_code_byte(emit, MP_BC_WITH_CLEANUP);
 }
 
 static void emit_bc_setup_except(emit_t *emit, int label) {
     emit_pre(emit, 6);
-    emit_write_byte_1_unsigned_label(emit, MP_BC_SETUP_EXCEPT, label);
+    emit_write_byte_code_byte_unsigned_label(emit, MP_BC_SETUP_EXCEPT, label);
 }
 
 static void emit_bc_setup_finally(emit_t *emit, int label) {
     emit_pre(emit, 6);
-    emit_write_byte_1_unsigned_label(emit, MP_BC_SETUP_FINALLY, label);
+    emit_write_byte_code_byte_unsigned_label(emit, MP_BC_SETUP_FINALLY, label);
 }
 
 static void emit_bc_end_finally(emit_t *emit) {
     emit_pre(emit, -1);
-    emit_write_byte_1(emit, MP_BC_END_FINALLY);
+    emit_write_byte_code_byte(emit, MP_BC_END_FINALLY);
 }
 
 static void emit_bc_get_iter(emit_t *emit) {
     emit_pre(emit, 0);
-    emit_write_byte_1(emit, MP_BC_GET_ITER);
+    emit_write_byte_code_byte(emit, MP_BC_GET_ITER);
 }
 
 static void emit_bc_for_iter(emit_t *emit, int label) {
     emit_pre(emit, 1);
-    emit_write_byte_1_unsigned_label(emit, MP_BC_FOR_ITER, label);
+    emit_write_byte_code_byte_unsigned_label(emit, MP_BC_FOR_ITER, label);
 }
 
 static void emit_bc_for_iter_end(emit_t *emit) {
@@ -513,99 +573,99 @@
 
 static void emit_bc_pop_block(emit_t *emit) {
     emit_pre(emit, 0);
-    emit_write_byte_1(emit, MP_BC_POP_BLOCK);
+    emit_write_byte_code_byte(emit, MP_BC_POP_BLOCK);
 }
 
 static void emit_bc_pop_except(emit_t *emit) {
     emit_pre(emit, 0);
-    emit_write_byte_1(emit, MP_BC_POP_EXCEPT);
+    emit_write_byte_code_byte(emit, MP_BC_POP_EXCEPT);
 }
 
 static void emit_bc_unary_op(emit_t *emit, rt_unary_op_t op) {
     emit_pre(emit, 0);
-    emit_write_byte_1_byte(emit, MP_BC_UNARY_OP, op);
+    emit_write_byte_code_byte_byte(emit, MP_BC_UNARY_OP, op);
 }
 
 static void emit_bc_binary_op(emit_t *emit, rt_binary_op_t op) {
     emit_pre(emit, -1);
-    emit_write_byte_1_byte(emit, MP_BC_BINARY_OP, op);
+    emit_write_byte_code_byte_byte(emit, MP_BC_BINARY_OP, op);
 }
 
 static void emit_bc_build_tuple(emit_t *emit, int n_args) {
     assert(n_args >= 0);
     emit_pre(emit, 1 - n_args);
-    emit_write_byte_1_uint(emit, MP_BC_BUILD_TUPLE, n_args);
+    emit_write_byte_code_byte_uint(emit, MP_BC_BUILD_TUPLE, n_args);
 }
 
 static void emit_bc_build_list(emit_t *emit, int n_args) {
     assert(n_args >= 0);
     emit_pre(emit, 1 - n_args);
-    emit_write_byte_1_uint(emit, MP_BC_BUILD_LIST, n_args);
+    emit_write_byte_code_byte_uint(emit, MP_BC_BUILD_LIST, n_args);
 }
 
 static void emit_bc_list_append(emit_t *emit, int list_stack_index) {
     assert(list_stack_index >= 0);
     emit_pre(emit, -1);
-    emit_write_byte_1_uint(emit, MP_BC_LIST_APPEND, list_stack_index);
+    emit_write_byte_code_byte_uint(emit, MP_BC_LIST_APPEND, list_stack_index);
 }
 
 static void emit_bc_build_map(emit_t *emit, int n_args) {
     assert(n_args >= 0);
     emit_pre(emit, 1);
-    emit_write_byte_1_uint(emit, MP_BC_BUILD_MAP, n_args);
+    emit_write_byte_code_byte_uint(emit, MP_BC_BUILD_MAP, n_args);
 }
 
 static void emit_bc_store_map(emit_t *emit) {
     emit_pre(emit, -2);
-    emit_write_byte_1(emit, MP_BC_STORE_MAP);
+    emit_write_byte_code_byte(emit, MP_BC_STORE_MAP);
 }
 
 static void emit_bc_map_add(emit_t *emit, int map_stack_index) {
     assert(map_stack_index >= 0);
     emit_pre(emit, -2);
-    emit_write_byte_1_uint(emit, MP_BC_MAP_ADD, map_stack_index);
+    emit_write_byte_code_byte_uint(emit, MP_BC_MAP_ADD, map_stack_index);
 }
 
 static void emit_bc_build_set(emit_t *emit, int n_args) {
     assert(n_args >= 0);
     emit_pre(emit, 1 - n_args);
-    emit_write_byte_1_uint(emit, MP_BC_BUILD_SET, n_args);
+    emit_write_byte_code_byte_uint(emit, MP_BC_BUILD_SET, n_args);
 }
 
 static void emit_bc_set_add(emit_t *emit, int set_stack_index) {
     assert(set_stack_index >= 0);
     emit_pre(emit, -1);
-    emit_write_byte_1_uint(emit, MP_BC_SET_ADD, set_stack_index);
+    emit_write_byte_code_byte_uint(emit, MP_BC_SET_ADD, set_stack_index);
 }
 
 static void emit_bc_build_slice(emit_t *emit, int n_args) {
     assert(n_args >= 0);
     emit_pre(emit, 1 - n_args);
-    emit_write_byte_1_uint(emit, MP_BC_BUILD_SLICE, n_args);
+    emit_write_byte_code_byte_uint(emit, MP_BC_BUILD_SLICE, n_args);
 }
 
 static void emit_bc_unpack_sequence(emit_t *emit, int n_args) {
     assert(n_args >= 0);
     emit_pre(emit, -1 + n_args);
-    emit_write_byte_1_uint(emit, MP_BC_UNPACK_SEQUENCE, n_args);
+    emit_write_byte_code_byte_uint(emit, MP_BC_UNPACK_SEQUENCE, n_args);
 }
 
 static void emit_bc_unpack_ex(emit_t *emit, int n_left, int n_right) {
     assert(n_left >=0 && n_right >= 0);
     emit_pre(emit, -1 + n_left + n_right + 1);
-    emit_write_byte_1_uint(emit, MP_BC_UNPACK_EX, n_left | (n_right << 8));
+    emit_write_byte_code_byte_uint(emit, MP_BC_UNPACK_EX, n_left | (n_right << 8));
 }
 
 static void emit_bc_make_function(emit_t *emit, scope_t *scope, int n_dict_params, int n_default_params) {
     assert(n_default_params == 0 && n_dict_params == 0);
     emit_pre(emit, 1);
-    emit_write_byte_1_uint(emit, MP_BC_MAKE_FUNCTION, scope->unique_code_id);
+    emit_write_byte_code_byte_uint(emit, MP_BC_MAKE_FUNCTION, scope->unique_code_id);
 }
 
 static void emit_bc_make_closure(emit_t *emit, scope_t *scope, int n_dict_params, int n_default_params) {
     assert(n_default_params == 0 && n_dict_params == 0);
     emit_pre(emit, 0);
-    emit_write_byte_1_uint(emit, MP_BC_MAKE_CLOSURE, scope->unique_code_id);
+    emit_write_byte_code_byte_uint(emit, MP_BC_MAKE_CLOSURE, scope->unique_code_id);
 }
 
 static void emit_bc_call_function(emit_t *emit, int n_positional, int n_keyword, bool have_star_arg, bool have_dbl_star_arg) {
@@ -631,7 +691,7 @@
             op = MP_BC_CALL_FUNCTION;
         }
     }
-    emit_write_byte_1_uint(emit, op, (n_keyword << 8) | n_positional); // TODO make it 2 separate uints
+    emit_write_byte_code_byte_uint(emit, op, (n_keyword << 8) | n_positional); // TODO make it 2 separate uints
 }
 
 static void emit_bc_call_method(emit_t *emit, int n_positional, int n_keyword, bool have_star_arg, bool have_dbl_star_arg) {
@@ -657,19 +717,19 @@
             op = MP_BC_CALL_METHOD;
         }
     }
-    emit_write_byte_1_uint(emit, op, (n_keyword << 8) | n_positional); // TODO make it 2 separate uints
+    emit_write_byte_code_byte_uint(emit, op, (n_keyword << 8) | n_positional); // TODO make it 2 separate uints
 }
 
 static void emit_bc_return_value(emit_t *emit) {
     emit_pre(emit, -1);
     emit->last_emit_was_return_value = true;
-    emit_write_byte_1(emit, MP_BC_RETURN_VALUE);
+    emit_write_byte_code_byte(emit, MP_BC_RETURN_VALUE);
 }
 
 static void emit_bc_raise_varargs(emit_t *emit, int n_args) {
     assert(0 <= n_args && n_args <= 2);
     emit_pre(emit, -n_args);
-    emit_write_byte_1_byte(emit, MP_BC_RAISE_VARARGS, n_args);
+    emit_write_byte_code_byte_byte(emit, MP_BC_RAISE_VARARGS, n_args);
 }
 
 static void emit_bc_yield_value(emit_t *emit) {
@@ -677,7 +737,7 @@
     if (emit->pass == PASS_2) {
         emit->scope->flags |= SCOPE_FLAG_GENERATOR;
     }
-    emit_write_byte_1(emit, MP_BC_YIELD_VALUE);
+    emit_write_byte_code_byte(emit, MP_BC_YIELD_VALUE);
 }
 
 static void emit_bc_yield_from(emit_t *emit) {
@@ -685,7 +745,7 @@
     if (emit->pass == PASS_2) {
         emit->scope->flags |= SCOPE_FLAG_GENERATOR;
     }
-    emit_write_byte_1(emit, MP_BC_YIELD_FROM);
+    emit_write_byte_code_byte(emit, MP_BC_YIELD_FROM);
 }
 
 const emit_method_table_t emit_bc_method_table = {
@@ -695,6 +755,7 @@
     emit_bc_last_emit_was_return_value,
     emit_bc_get_stack_size,
     emit_bc_set_stack_size,
+    emit_bc_set_source_line,
 
     emit_bc_load_id,
     emit_bc_store_id,
diff --git a/py/emitcpy.c b/py/emitcpy.c
index ee96e58..42eef91 100644
--- a/py/emitcpy.c
+++ b/py/emitcpy.c
@@ -68,6 +68,9 @@
     emit->stack_size = size;
 }
 
+static void emit_cpy_set_source_line(emit_t *emit, int source_line) {
+}
+
 static void emit_cpy_load_id(emit_t *emit, qstr qstr) {
     emit_common_load_id(emit, &emit_cpython_method_table, emit->scope, qstr);
 }
@@ -798,6 +801,7 @@
     emit_cpy_last_emit_was_return_value,
     emit_cpy_get_stack_size,
     emit_cpy_set_stack_size,
+    emit_cpy_set_source_line,
 
     emit_cpy_load_id,
     emit_cpy_store_id,
diff --git a/py/emitnative.c b/py/emitnative.c
index aea25ac..a80cd2c 100644
--- a/py/emitnative.c
+++ b/py/emitnative.c
@@ -281,6 +281,9 @@
     emit->stack_size = size;
 }
 
+static void emit_native_set_source_line(emit_t *emit, int source_line) {
+}
+
 static void adjust_stack(emit_t *emit, int stack_size_delta) {
     emit->stack_size += stack_size_delta;
     assert(emit->stack_size >= 0);
@@ -1228,6 +1231,7 @@
     emit_native_last_emit_was_return_value,
     emit_native_get_stack_size,
     emit_native_set_stack_size,
+    emit_native_set_source_line,
 
     emit_native_load_id,
     emit_native_store_id,
diff --git a/py/emitpass1.c b/py/emitpass1.c
index 60fdd0b..c73522e 100644
--- a/py/emitpass1.c
+++ b/py/emitpass1.c
@@ -103,6 +103,7 @@
     (void*)emit_pass1_dummy,
     (void*)emit_pass1_dummy,
     (void*)emit_pass1_dummy,
+    (void*)emit_pass1_dummy,
 
     emit_pass1_load_id,
     emit_pass1_store_id,
diff --git a/py/lexer.c b/py/lexer.c
index 6feb231..e8c6bc3 100644
--- a/py/lexer.c
+++ b/py/lexer.c
@@ -3,6 +3,7 @@
 
 #include <stdint.h>
 #include <stdio.h>
+#include <string.h>
 #include <assert.h>
 
 #include "misc.h"
@@ -14,7 +15,7 @@
 // don't know if that's intentional or not, but we don't allow it
 
 struct _mp_lexer_t {
-    const char *name;           // name of source
+    qstr source_name;           // name of source
     void *stream_data;          // data for stream
     mp_lexer_stream_next_char_t stream_next_char;   // stream callback to get next char
     mp_lexer_stream_close_t stream_close;           // stream callback to free
@@ -49,7 +50,7 @@
 }
 
 void mp_token_show(const mp_token_t *tok) {
-    printf("(%s:%d:%d) kind:%d str:%p len:%d", tok->src_name, tok->src_line, tok->src_column, tok->kind, tok->str, tok->len);
+    printf("(%d:%d) kind:%d str:%p len:%d", tok->src_line, tok->src_column, tok->kind, tok->str, tok->len);
     if (tok->str != NULL && tok->len > 0) {
         const char *i = tok->str;
         const char *j = i + tok->len;
@@ -292,7 +293,6 @@
             next_char(lex);
             if (!is_physical_newline(lex)) {
                 // SyntaxError: unexpected character after line continuation character
-                tok->src_name = lex->name;
                 tok->src_line = lex->line;
                 tok->src_column = lex->column;
                 tok->kind = MP_TOKEN_BAD_LINE_CONTINUATION;
@@ -309,7 +309,6 @@
     }
 
     // set token source information
-    tok->src_name = lex->name;
     tok->src_line = lex->line;
     tok->src_column = lex->column;
 
@@ -594,7 +593,7 @@
 mp_lexer_t *mp_lexer_new(const char *src_name, void *stream_data, mp_lexer_stream_next_char_t stream_next_char, mp_lexer_stream_close_t stream_close) {
     mp_lexer_t *lex = m_new(mp_lexer_t, 1);
 
-    lex->name = src_name; // TODO do we need to strdup this?
+    lex->source_name = qstr_from_strn_copy(src_name, strlen(src_name));
     lex->stream_data = stream_data;
     lex->stream_next_char = stream_next_char;
     lex->stream_close = stream_close;
@@ -642,6 +641,10 @@
     }
 }
 
+qstr mp_lexer_source_name(mp_lexer_t *lex) {
+    return lex->source_name;
+}
+
 void mp_lexer_to_next(mp_lexer_t *lex) {
     mp_lexer_next_token_into(lex, &lex->tok_cur, false);
 }
@@ -677,11 +680,11 @@
 */
 
 bool mp_lexer_show_error_pythonic_prefix(mp_lexer_t *lex) {
-    printf("  File \"%s\", line %d column %d\n", lex->tok_cur.src_name, lex->tok_cur.src_line, lex->tok_cur.src_column);
+    printf("  File \"%s\", line %d column %d\n", qstr_str(lex->source_name), lex->tok_cur.src_line, lex->tok_cur.src_column);
     return false;
 }
 
 bool mp_lexer_show_error_pythonic(mp_lexer_t *lex, const char *msg) {
-    printf("  File \"%s\", line %d column %d\n%s\n", lex->tok_cur.src_name, lex->tok_cur.src_line, lex->tok_cur.src_column, msg);
+    printf("  File \"%s\", line %d column %d\n%s\n", qstr_str(lex->source_name), lex->tok_cur.src_line, lex->tok_cur.src_column, msg);
     return false;
 }
diff --git a/py/lexer.h b/py/lexer.h
index ea928c7..69e9732 100644
--- a/py/lexer.h
+++ b/py/lexer.h
@@ -105,7 +105,6 @@
 } mp_token_kind_t;
 
 typedef struct _mp_token_t {
-    const char *src_name;       // name of source
     uint src_line;              // source line
     uint src_column;            // source column
 
@@ -129,6 +128,7 @@
 mp_lexer_t *mp_lexer_new_from_str_len(const char *src_name, const char *str, uint len, uint free_len);
 
 void mp_lexer_free(mp_lexer_t *lex);
+qstr mp_lexer_source_name(mp_lexer_t *lex);
 void mp_lexer_to_next(mp_lexer_t *lex);
 const mp_token_t *mp_lexer_cur(const mp_lexer_t *lex);
 bool mp_lexer_is_kind(mp_lexer_t *lex, mp_token_kind_t kind);
diff --git a/py/obj.h b/py/obj.h
index 5691f09..4690f6b 100644
--- a/py/obj.h
+++ b/py/obj.h
@@ -273,6 +273,8 @@
 // exception
 extern const mp_obj_type_t exception_type;
 qstr mp_obj_exception_get_type(mp_obj_t self_in);
+void mp_obj_exception_set_source_info(mp_obj_t self_in, qstr file, machine_uint_t line);
+void mp_obj_exception_get_source_info(mp_obj_t self_in, qstr *file, machine_uint_t *line);
 
 // str
 extern const mp_obj_type_t str_type;
diff --git a/py/objexcept.c b/py/objexcept.c
index 1d30758..7f87478 100644
--- a/py/objexcept.c
+++ b/py/objexcept.c
@@ -17,6 +17,8 @@
 // have args tuple (or otherwise have it as NULL).
 typedef struct mp_obj_exception_t {
     mp_obj_base_t base;
+    qstr source_file;
+    machine_uint_t source_line;
     qstr id;
     qstr msg;
     mp_obj_tuple_t args;
@@ -87,6 +89,8 @@
     // make exception object
     mp_obj_exception_t *o = m_new_obj_var(mp_obj_exception_t, mp_obj_t*, 0);
     o->base.type = &exception_type;
+    o->source_file = 0;
+    o->source_line = 0;
     o->id = id;
     o->args.len = 0;
     if (fmt == NULL) {
@@ -109,3 +113,23 @@
     mp_obj_exception_t *self = self_in;
     return self->id;
 }
+
+void mp_obj_exception_set_source_info(mp_obj_t self_in, qstr file, machine_uint_t line) {
+    assert(MP_OBJ_IS_TYPE(self_in, &exception_type));
+    mp_obj_exception_t *self = self_in;
+    // TODO make a list of file/line pairs for the traceback
+    // for now, just keep the first one
+    if (file != 0 && self->source_file == 0) {
+        self->source_file = file;
+    }
+    if (line != 0 && self->source_line == 0) {
+        self->source_line = line;
+    }
+}
+
+void mp_obj_exception_get_source_info(mp_obj_t self_in, qstr *file, machine_uint_t *line) {
+    assert(MP_OBJ_IS_TYPE(self_in, &exception_type));
+    mp_obj_exception_t *self = self_in;
+    *file = self->source_file;
+    *line = self->source_line;
+}
diff --git a/py/objgenerator.c b/py/objgenerator.c
index d58480f..2e8bd3d 100644
--- a/py/objgenerator.c
+++ b/py/objgenerator.c
@@ -58,6 +58,7 @@
 
 typedef struct _mp_obj_gen_instance_t {
     mp_obj_base_t base;
+    const byte *code_info;
     const byte *ip;
     mp_obj_t *sp;
     uint n_state;
@@ -74,7 +75,7 @@
 
 mp_obj_t gen_instance_iternext(mp_obj_t self_in) {
     mp_obj_gen_instance_t *self = self_in;
-    bool yield = mp_execute_byte_code_2(&self->ip, &self->state[self->n_state - 1], &self->sp);
+    bool yield = mp_execute_byte_code_2(self->code_info, &self->ip, &self->state[self->n_state - 1], &self->sp);
     if (yield) {
         return *self->sp;
     } else {
@@ -98,6 +99,7 @@
 mp_obj_t mp_obj_new_gen_instance(const byte *bytecode, uint n_state, int n_args, const mp_obj_t *args) {
     mp_obj_gen_instance_t *o = m_new_obj_var(mp_obj_gen_instance_t, mp_obj_t, n_state);
     o->base.type = &gen_instance_type;
+    o->code_info = bytecode;
     o->ip = bytecode;
     o->sp = &o->state[0] - 1; // sp points to top of stack, which starts off 1 below the state
     o->n_state = n_state;
@@ -111,6 +113,10 @@
     // prelude for making cells (closed over variables)
     // for now we just make sure there are no cells variables
     // need to work out how to implement closed over variables in generators
+
+    // get code info size
+    machine_uint_t code_info_size = bytecode[0] | (bytecode[1] << 8) | (bytecode[2] << 16) | (bytecode[3] << 24);
+    o->ip += code_info_size;
     assert(o->ip[0] == 0);
     o->ip += 1;
 
diff --git a/py/parse.c b/py/parse.c
index 49b42e5..fc74a5f 100644
--- a/py/parse.c
+++ b/py/parse.c
@@ -80,7 +80,8 @@
 };
 
 typedef struct _rule_stack_t {
-    byte rule_id;
+    unsigned int src_line : 24;
+    unsigned int rule_id : 8;
     int32_t arg_i; // what should be the size and signedness?
 } rule_stack_t;
 
@@ -92,45 +93,54 @@
     uint result_stack_alloc;
     uint result_stack_top;
     mp_parse_node_t *result_stack;
+
+    mp_lexer_t *lexer;
 } parser_t;
 
-static void push_rule(parser_t *parser, const rule_t *rule, int arg_i) {
+static void push_rule(parser_t *parser, int src_line, const rule_t *rule, int arg_i) {
     if (parser->rule_stack_top >= parser->rule_stack_alloc) {
         parser->rule_stack = m_renew(rule_stack_t, parser->rule_stack, parser->rule_stack_alloc, parser->rule_stack_alloc * 2);
         parser->rule_stack_alloc *= 2;
     }
-    parser->rule_stack[parser->rule_stack_top].rule_id = rule->rule_id;
-    parser->rule_stack[parser->rule_stack_top].arg_i = arg_i;
-    parser->rule_stack_top += 1;
+    rule_stack_t *rs = &parser->rule_stack[parser->rule_stack_top++];
+    rs->src_line = src_line;
+    rs->rule_id = rule->rule_id;
+    rs->arg_i = arg_i;
 }
 
 static void push_rule_from_arg(parser_t *parser, uint arg) {
     assert((arg & RULE_ARG_KIND_MASK) == RULE_ARG_RULE || (arg & RULE_ARG_KIND_MASK) == RULE_ARG_OPT_RULE);
     uint rule_id = arg & RULE_ARG_ARG_MASK;
     assert(rule_id < RULE_maximum_number_of);
-    push_rule(parser, rules[rule_id], 0);
+    push_rule(parser, mp_lexer_cur(parser->lexer)->src_line, rules[rule_id], 0);
 }
 
-static void pop_rule(parser_t *parser, const rule_t **rule, uint *arg_i) {
+static void pop_rule(parser_t *parser, const rule_t **rule, uint *arg_i, uint *src_line) {
     parser->rule_stack_top -= 1;
     *rule = rules[parser->rule_stack[parser->rule_stack_top].rule_id];
     *arg_i = parser->rule_stack[parser->rule_stack_top].arg_i;
+    *src_line = parser->rule_stack[parser->rule_stack_top].src_line;
 }
 
 mp_parse_node_t mp_parse_node_new_leaf(machine_int_t kind, machine_int_t arg) {
     return (mp_parse_node_t)(kind | (arg << 4));
 }
 
-int num_parse_nodes_allocated = 0;
-mp_parse_node_struct_t *parse_node_new_struct(int rule_id, int num_args) {
+//int num_parse_nodes_allocated = 0;
+mp_parse_node_struct_t *parse_node_new_struct(int src_line, int rule_id, int num_args) {
     mp_parse_node_struct_t *pn = m_new_obj_var(mp_parse_node_struct_t, mp_parse_node_t, num_args);
-    pn->source = 0; // TODO
+    pn->source_line = src_line;
     pn->kind_num_nodes = (rule_id & 0xff) | (num_args << 8);
-    num_parse_nodes_allocated += 1;
+    //num_parse_nodes_allocated += 1;
     return pn;
 }
 
 void mp_parse_node_show(mp_parse_node_t pn, int indent) {
+    if (MP_PARSE_NODE_IS_STRUCT(pn)) {
+        printf("[% 4d] ", (int)((mp_parse_node_struct_t*)pn)->source_line);
+    } else {
+        printf("       ");
+    }
     for (int i = 0; i < indent; i++) {
         printf(" ");
     }
@@ -258,8 +268,8 @@
     push_result_node(parser, pn);
 }
 
-static void push_result_rule(parser_t *parser, const rule_t *rule, int num_args) {
-    mp_parse_node_struct_t *pn = parse_node_new_struct(rule->rule_id, num_args);
+static void push_result_rule(parser_t *parser, int src_line, const rule_t *rule, int num_args) {
+    mp_parse_node_struct_t *pn = parse_node_new_struct(src_line, rule->rule_id, num_args);
     for (int i = num_args; i > 0; i--) {
         pn->nodes[i - 1] = pop_result(parser);
     }
@@ -280,6 +290,8 @@
     parser->result_stack_top = 0;
     parser->result_stack = m_new(mp_parse_node_t, parser->result_stack_alloc);
 
+    parser->lexer = lex;
+
     // work out the top-level rule to use, and push it on the stack
     int top_level_rule;
     switch (input_kind) {
@@ -287,13 +299,14 @@
         case MP_PARSE_EVAL_INPUT: top_level_rule = RULE_eval_input; break;
         default: top_level_rule = RULE_file_input;
     }
-    push_rule(parser, rules[top_level_rule], 0);
+    push_rule(parser, mp_lexer_cur(lex)->src_line, rules[top_level_rule], 0);
 
     // parse!
 
-    uint n, i;
+    uint n, i; // state for the current rule
+    uint rule_src_line; // source line for the first token matched by the current rule
     bool backtrack = false;
-    const rule_t *rule;
+    const rule_t *rule = NULL;
     mp_token_kind_t tok_kind;
     bool emit_rule;
     bool had_trailing_sep;
@@ -304,7 +317,7 @@
             break;
         }
 
-        pop_rule(parser, &rule, &i);
+        pop_rule(parser, &rule, &i, &rule_src_line);
         n = rule->act & RULE_ACT_ARG_MASK;
 
         /*
@@ -333,8 +346,8 @@
                             }
                             break;
                         case RULE_ARG_RULE:
-                            push_rule(parser, rule, i + 1);
-                            push_rule_from_arg(parser, rule->arg[i]);
+                            push_rule(parser, rule_src_line, rule, i + 1); // save this or-rule
+                            push_rule_from_arg(parser, rule->arg[i]); // push child of or-rule
                             goto next_rule;
                         default:
                             assert(0);
@@ -398,14 +411,9 @@
                             }
                             break;
                         case RULE_ARG_RULE:
-                            //if (i + 1 < n) {
-                                push_rule(parser, rule, i + 1);
-                            //}
-                            push_rule_from_arg(parser, rule->arg[i]);
-                            goto next_rule;
                         case RULE_ARG_OPT_RULE:
-                            push_rule(parser, rule, i + 1);
-                            push_rule_from_arg(parser, rule->arg[i]);
+                            push_rule(parser, rule_src_line, rule, i + 1); // save this and-rule
+                            push_rule_from_arg(parser, rule->arg[i]); // push child of and-rule
                             goto next_rule;
                         default:
                             assert(0);
@@ -462,9 +470,9 @@
                 }
                 //printf("done and %s n=%d i=%d notnil=%d\n", rule->rule_name, n, i, num_not_nil);
                 if (emit_rule) {
-                    push_result_rule(parser, rule, i);
+                    push_result_rule(parser, rule_src_line, rule, i);
                 } else if (num_not_nil == 0) {
-                    push_result_rule(parser, rule, i); // needed for, eg, atom_paren, testlist_comp_3b
+                    push_result_rule(parser, rule_src_line, rule, i); // needed for, eg, atom_paren, testlist_comp_3b
                     //result_stack_show(parser);
                     //assert(0);
                 } else if (num_not_nil == 1) {
@@ -478,7 +486,7 @@
                     }
                     push_result_node(parser, pn);
                 } else {
-                    push_result_rule(parser, rule, i);
+                    push_result_rule(parser, rule_src_line, rule, i);
                 }
                 break;
 
@@ -538,8 +546,8 @@
                                 }
                                 break;
                             case RULE_ARG_RULE:
-                                push_rule(parser, rule, i + 1);
-                                push_rule_from_arg(parser, arg);
+                                push_rule(parser, rule_src_line, rule, i + 1); // save this list-rule
+                                push_rule_from_arg(parser, arg); // push child of list-rule
                                 goto next_rule;
                             default:
                                 assert(0);
@@ -559,13 +567,13 @@
                     // list matched single item
                     if (had_trailing_sep) {
                         // if there was a trailing separator, make a list of a single item
-                        push_result_rule(parser, rule, i);
+                        push_result_rule(parser, rule_src_line, rule, i);
                     } else {
                         // just leave single item on stack (ie don't wrap in a list)
                     }
                 } else {
                     //printf("done list %s %d %d\n", rule->rule_name, n, i);
-                    push_result_rule(parser, rule, i);
+                    push_result_rule(parser, rule_src_line, rule, i);
                 }
                 break;
 
diff --git a/py/parse.h b/py/parse.h
index be2073a..e1e7f73 100644
--- a/py/parse.h
+++ b/py/parse.h
@@ -28,7 +28,7 @@
 typedef machine_uint_t mp_parse_node_t; // must be pointer size
 
 typedef struct _mp_parse_node_struct_t {
-    uint32_t source;            // file identifier, and line number
+    uint32_t source_line;       // line number in source file
     uint32_t kind_num_nodes;    // parse node kind, and number of nodes
     mp_parse_node_t nodes[];    // nodes
 } mp_parse_node_struct_t;
diff --git a/py/showbc.c b/py/showbc.c
index 36393ce..ba7c309 100644
--- a/py/showbc.c
+++ b/py/showbc.c
@@ -18,6 +18,10 @@
 void mp_show_byte_code(const byte *ip, int len) {
     const byte *ip_start = ip;
 
+    // get code info size
+    machine_uint_t code_info_size = ip[0] | (ip[1] << 8) | (ip[2] << 16) | (ip[3] << 24);
+    ip += code_info_size;
+
     // decode prelude
     {
         uint n_local = *ip++;
diff --git a/py/vm.c b/py/vm.c
index f352b12..cacb6ac 100644
--- a/py/vm.c
+++ b/py/vm.c
@@ -38,8 +38,13 @@
         assert(i < 8);
         state[n_state - 1 - i] = args[i];
     }
+
     const byte *ip = code;
 
+    // get code info size
+    machine_uint_t code_info_size = ip[0] | (ip[1] << 8) | (ip[2] << 16) | (ip[3] << 24);
+    ip += code_info_size;
+
     // execute prelude to make any cells (closed over variables)
     {
         for (uint n_local = *ip++; n_local > 0; n_local--) {
@@ -53,7 +58,7 @@
     }
 
     // execute the byte code
-    if (mp_execute_byte_code_2(&ip, &state[n_state - 1], &sp)) {
+    if (mp_execute_byte_code_2(code, &ip, &state[n_state - 1], &sp)) {
         // it shouldn't yield
         assert(0);
     }
@@ -65,7 +70,7 @@
 
 // fastn has items in reverse order (fastn[0] is local[0], fastn[-1] is local[1], etc)
 // sp points to bottom of stack which grows up
-bool mp_execute_byte_code_2(const byte **ip_in_out, mp_obj_t *fastn, mp_obj_t **sp_in_out) {
+bool mp_execute_byte_code_2(const byte *code_info, const byte **ip_in_out, mp_obj_t *fastn, mp_obj_t **sp_in_out) {
     // careful: be sure to declare volatile any variables read in the exception handler (written is ok, I think)
 
     const byte *ip = *ip_in_out;
@@ -79,12 +84,14 @@
     volatile machine_uint_t currently_in_except_block = 0; // 0 or 1, to detect nested exceptions
     machine_uint_t exc_stack[8]; // on the exception stack we store (ip, sp | X) for each block, X = previous value of currently_in_except_block
     machine_uint_t *volatile exc_sp = &exc_stack[0] - 1; // stack grows up, exc_sp points to top of stack
+    const byte *volatile save_ip = ip; // this is so we can access ip in the exception handler without making ip volatile (which means the compiler can't keep it in a register in the main loop)
 
     // outer exception handling loop
     for (;;) {
         if (nlr_push(&nlr) == 0) {
             // loop to execute byte code
             for (;;) {
+                save_ip = ip;
                 int op = *ip++;
                 switch (op) {
                     case MP_BC_LOAD_CONST_FALSE:
@@ -518,6 +525,23 @@
         } else {
             // exception occurred
 
+            // set file and line number that the exception occurred at
+            if (MP_OBJ_IS_TYPE(nlr.ret_val, &exception_type)) {
+                machine_uint_t code_info_size = code_info[0] | (code_info[1] << 8) | (code_info[2] << 16) | (code_info[3] << 24);
+                qstr = code_info[4] | (code_info[5] << 8) | (code_info[6] << 16) | (code_info[7] << 24);
+                machine_uint_t source_line = 1;
+                machine_uint_t bc = save_ip - code_info - code_info_size;
+                //printf("find %lu %d %d\n", bc, code_info[8], code_info[9]);
+                for (const byte* ci = code_info + 8; bc > ci[0]; ci += 2) {
+                    bc -= ci[0];
+                    source_line += ci[1];
+                    if (ci[0] == 0 && ci[1] == 0) {
+                        break;
+                    }
+                }
+                mp_obj_exception_set_source_info(nlr.ret_val, qstr, source_line);
+            }
+
             while (currently_in_except_block) {
                 // nested exception