step.py

import re

from IPython.core.magic import Magics, magics_class, line_magic
from IPython.core.debugger import Pdb

ipdb = Pdb()

@magics_class
class StepMagic(Magics):

  @line_magic
  def step(self, params):
    # params might either be
    # foo, bar, baz
    # or
    # foo(bar, baz)
    # we need to determine if there is a comma before the opening paren.
    comma_pos = params.find(',')
    paren_pos = params.find(')')
    if comma_pos > -1 and (comma_pos < paren_pos or paren_pos == -1):
      param_list = params.split(',')
    else:
      # Match everything up to first open paren, and everything inside parens.
      # We use lazy repetition on the first group to ensure that it copes when
      # the expressions within the parens are themselves calls.
      match = re.match(r'(.*?)\((.*)\)', params)
      if match:
        func, args = match.groups()
        # TODO: this doesn't work when args consists of a tuple.
        param_list = [func] + args.split(',')
      else:
        # Assume it's a single expression
        param_list = [params]

    evaluated_params = [self.shell.ev(p) for p in param_list]
    ipdb.runcall(*evaluated_params)


_loaded = False

def load_ipython_extension(ip):
    """Load the extension in IPython."""
    global _loaded
    if not _loaded:
        plugin = StepMagic(shell=ip)
        ip.register_magics(plugin)
        _loaded = True