title: Python regex - conditional matching?
body: <p>I don't know if that's the right word for it, but I am trying to come up with some regex's that can extract coefficients and exponents from a mathematical expression.  The expression will come in the form 'axB+cxD+exF' where the lower case letters are the coefficients and the uppercase letters are the exponents.  I have a regex that can match to both of them, but I'm wondering if I can use 2 regexs, one to match the coefficients and one for the exponents.  Is there a way to match a number with a letter on one side of it without matching the letter?  EG, in '3x3+6x2+2x1+8x0' I need to get
      ['3', '6', '2', '8']
  and
      ['3', '2', '1', '0']</p>