This is a work-in-progress for some future cohpy meeting.

Lastly, uses names to refer to parts of a string that match a regular expression is fantastic! It makes the code much more readable than using meaningless numerical indexes.

This was new to a Python expert who now loves it, although his still prefers to eschew regular expressions because they are hard to read.

Imagine the following contrived example, where I want to get the hash of an git object from its filepath.



In [1]:

    
s = '.git/objects/8e/28241360c472576e8caa944253d4af368d9081'

import re
git_pattern = re.compile(r'''
    .*/                      # anything and a slash
    (
        ([0-9a-fA-F]{2})     # 2 hexadecimal digits
        /                    # separated by a slash
        ([0-9a-fA-F]{38})    # 38 hexadecimal digits
    )$''', flags=re.VERBOSE)



In [2]:

    
m = git_pattern.match(s)
m









    Out[2]:





<_sre.SRE_Match object; span=(0, 54), match='.git/objects/8e/28241360c472576e8caa944253d4af368>



In [3]:

    
m.group(0)









    Out[3]:





'.git/objects/8e/28241360c472576e8caa944253d4af368d9081'



In [4]:

    
m.group(1)









    Out[4]:





'8e/28241360c472576e8caa944253d4af368d9081'



In [5]:

    
m.group(2)









    Out[5]:





'8e'



In [6]:

    
m.group(3)









    Out[6]:





'28241360c472576e8caa944253d4af368d9081'



In [7]:

    
help(re.compile)









    



Help on function compile in module re:

compile(pattern, flags=0)
    Compile a regular expression pattern, returning a pattern object.



In [8]:

    
s = '.git/objects/8e/28241360c472576e8caa944253d4af368d9081'

import re
git_pattern = re.compile(r'''
    .*/                      # anything and a slash
    (?P<hash_with_slash>
        (?P<hash_directory> [0-9a-fA-F]{2})     # 2 hexadecimal digits
        /                    # separated by a slash
        (?P<hash_filename> [0-9a-fA-F]{38})    # 38 hexadecimal digits
    )$''', flags=re.VERBOSE)



In [9]:

    
m = git_pattern.match(s)
m









    Out[9]:





<_sre.SRE_Match object; span=(0, 54), match='.git/objects/8e/28241360c472576e8caa944253d4af368>



In [10]:

    
m.group(2)









    Out[10]:





'8e'



In [11]:

    
m.group('hash_directory')









    Out[11]:





'8e'



In [12]:

    
m.group(3)









    Out[12]:





'28241360c472576e8caa944253d4af368d9081'



In [13]:

    
m.group('hash_filename')









    Out[13]:





'28241360c472576e8caa944253d4af368d9081'



In [14]:

    
hash = m.group('hash_directory') + m.group('hash_filename')
hash









    Out[14]:





'8e28241360c472576e8caa944253d4af368d9081'



In [15]:

    
hash = ''.join(map(m.group, ('hash_directory', 'hash_filename')))
hash









    Out[15]:





'8e28241360c472576e8caa944253d4af368d9081'



In [16]:

    
hash = ''.join(map(lambda s: m.group('hash_%s' % s), ('directory', 'filename')))
hash









    Out[16]:





'8e28241360c472576e8caa944253d4af368d9081'



In [17]:

    
m.group(1)









    Out[17]:





'8e/28241360c472576e8caa944253d4af368d9081'



In [18]:

    
m.group('hash_with_slash')









    Out[18]:





'8e/28241360c472576e8caa944253d4af368d9081'



In [19]:

    
hash = ''.join(c for c in m.group('hash_with_slash') if c != '/')
hash









    Out[19]:





'8e28241360c472576e8caa944253d4af368d9081'



In [20]:

    
s









    Out[20]:





'.git/objects/8e/28241360c472576e8caa944253d4af368d9081'



In [21]:

    
s = '8e/28241360c472576e8caa944253d4af368d9081'
m = git_pattern.match(s)
m



In [22]:

    
repr(m)









    Out[22]:





'None'