decode Data URI to mime and data parts

gistfile1.py

import base64

def decodeDataUri(uristr):
  comma = uristr.find(',')
  urihead = uristr.find('data:')

  if urihead is None or comma is None:
    return None
  headpart = uristr[urihead + 5:comma]
  firstsep = headpart.find(';')
  
  if firstsep is None:
    firstsep = len(firstsep)
  
  mimetype = headpart[0:firstsep]
	
  b64data = uristr[(comma + 1):]

  rawdata = base64.b64decode(b64data)	

  return ( mimetype, rawdata )