debug: a little easier to get code samples from tests

Author: nedbat

lab/extract_code.py

@@ -50,7 +50,10 @@ def f(a, b):
 import sys
 import textwrap
 
-fname, lineno = sys.argv[1:]
+if len(sys.argv) == 2:
+    fname, lineno = sys.argv[1].split(":")
+else:
+    fname, lineno = sys.argv[1:]
 lineno = int(lineno)
 
 with open(fname) as code_file: