Pushing Python introspection to limits

Question

Simple question – can I print the source code of this if?

if __name__ == '__main__':
  # ...
  # this is the `if` I want to print
  #  V 
  if args and args[0][0] == '-':
    if args[0] in ('--help','-h','-?'):
      print_source_of_block(level=2)
    icase = 'i' in args[0]
    desc = 'd' in args[0]
    args = args[1:]

Please don't ask me why I need it, nor give me advice on how to write user help. I want to know it because I'm curious.

Answer 1

Yeah, that's doable. Here's a quick sketch of how you could do it and what tools would be involved:

1. Retrieve the stack frame of print_source_of_block's caller with inspect.currentframe().f_back.
2. Determine the caller's source file and line number within that source file with inspect.getframeinfo.
3. Open the source file.
4. Either
   • Use ast.parse to parse the file, or
   • Use tokenize.tokenize to tokenize it.
5. Using either the abstract syntax tree or the token stream, determine where the requested source block begins and ends.
6. Print the block.