vim can be a powerful tool for visualizing regular expressions as well. paste in the text and set incsearch and set hlsearch to match on partial expressions and highlight matches. this allows you to distinctly see the effects of a regex as you type it.

also, python's regex module can show you how it interprets a regular expression by passing the re.DEBUG flag to re.compile:

  >>> import re
  >>> re.compile('a*b+', re.DEBUG)
  max_repeat 0 65535
    literal 97
  max_repeat 1 65535
    literal 98
  <_sre.SRE_Pattern object at 0x100460230>