Convert, or unformat, a string to variables (like format(), but in reverse) in Python

Question

I have strings of the form Version 1.4.0\n and Version 1.15.6\n, and I'd like a simple way of extracting the three numbers from them. I know I can put variables into a string with the format method; I basically want to do that backwards, like this:

# So I know I can do this: x, y, z = 1, 4, 0 print 'Version {0}.{1}.{2}\n'.format(x,y,z) # Output is 'Version 1.4.0\n'  # But I'd like to be able to reverse it:  mystr='Version 1.15.6\n' a, b, c = mystr.unformat('Version {0}.{1}.{2}\n')  # And have the result that a, b, c = 1, 15, 6 

Someone else I found asked the same question, but the reply was specific to their particular case: Use Python format string in reverse for parsing

A general answer (how to do format() in reverse) would be great! An answer for my specific case would be very helpful too though.

Answer 1

Just to build on Uche's answer, I was looking for a way to reverse a string via a pattern with kwargs. So I put together the following function:

def string_to_dict(string, pattern):     regex = re.sub(r'{(.+?)}', r'(?P<_\1>.+)', pattern)     values = list(re.search(regex, string).groups())     keys = re.findall(r'{(.+?)}', pattern)     _dict = dict(zip(keys, values))     return _dict 

Which works as per:

>>> p = 'hello, my name is {name} and I am a {age} year old {what}'  >>> s = p.format(name='dan', age=33, what='developer') >>> s 'hello, my name is dan and I am a 33 year old developer' >>> string_to_dict(s, p) {'age': '33', 'name': 'dan', 'what': 'developer'}  >>> s = p.format(name='cody', age=18, what='quarterback') >>> s 'hello, my name is cody and I am a 18 year old quarterback' >>> string_to_dict(s, p) {'age': '18', 'name': 'cody', 'what': 'quarterback'} 

Answer 2

>>> import re >>> re.findall('(\d+)\.(\d+)\.(\d+)', 'Version 1.15.6\n') [('1', '15', '6')]