Parse the format specification (https://docs.python.org/2.7/library/string.html#format-specification-mini-language) from a .format style python string

parse_fspec.py

import re
from string import Formatter

_fspecre = ("((?P<fill>{fill})?(?P<align>{align}))?"
            "(?P<sign>{sign})?"
            "(?P<prefix>#)?"
            "(?P<zeropad>0)?"
            "(?P<width>{width})?"
            "(?P<thousands>,)?"
            "(?:\.(?P<precision>{precision}))?"
            "(?P<type>{type})?")
_fspecre = _fspecre.format( fill='.',
                            align="<|>|=|^",
                            sign="\+|-| ",
                            width="[0-9]+",
                            precision="[0-9]+",
                            type=r"b|c|d|e|E|f|F|g|G|n|o|s|x|X|%")
_fspecre = re.compile(_fspecre)
_format = Formatter()

def parse(fmt):
    parsed = list(_format.parse(fmt))

    if len(parsed) == 1:
        parsed = [parsed]

    for lit, fieldname, fspec, conv in parsed:
        if fspec is not None:
            fspec = _fspecre.match(fspec).groupdict()

        yield lit, fieldname, fspec, conv