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Parser regex from named group

Here's a rough expression I'm working with /api/(?P<version>v[0-9]+)/endpoint

.

I would like to do two things:

  • Get named groups, i.e. version

  • For named groups, get the associated expression, i.e. v[0-9]+

The first part can be grabbed from the compiled regex:

>>> r = re.compile('/api/(?P<version>v[0-9]+)/endpoint')
>>> r.groupindex 
{'version': 1}

I am wondering if there is anything that will allow me to grab an expression from a parsing group, for example.

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2 answers


You can create a base class that takes a template string, some parameters that are populated with kwargs (or a dictionary), then proxies all the other access attributes of the compiled regex like:

import re

class myre(object):
    def __init__(self, template, *args, **kwargs):
        self.expressions = dict(kwargs)
        subs = {k: '(?P<{}>{})'.format(k, v) for k, v in self.expressions.items()}
        self.rx = re.compile(template.format(**subs), *args)
    def __getattr__(self, name):
        return getattr(self.rx, name)


Then use the following:

r = myre('/api/{version}/endpoint', version='v[0-9]+')
print r.expressions['version'] # get expression for named group
# v[0-9]+

print list(r.expressions) # get list of named groups
# ['version']

# match as normal
print r.match('/api/v5/endpoint').group('version')
# v5
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You will need to implement this yourself. For example:

group = {'version': 'v[0-9]+'}
r = re.compile('/api/(?P<{}>{})/endpoint'.format('version', group['version']))


Later you can match the group name version

with its regexv[0-9]+

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