[issue2551053] REST-API: Regular expressions used as keys in dictionary

New submission from Ralf Schlatterbeck:

The __route_map dictionary takes regular expressions as keys of a
dictionary. Now the regular expression implementation (at least in
python2) has a cache, so usually returns the same object for the same
regex (plus options) for calls to re.compile.

But this doesn't seem to work in all cases, we're observing a dictionary
with multiple entries for the *same* regular expression with different
methods in a WSGI process in apache, e.g.

^rest/data/([\\w.\\-~!$&'()*+,;=:\\%%]+)$ ['POST', 'GET']
^rest/data/([\\w.\\-~!$&'()*+,;=:\\%%]+)$ ['OPTIONS', 'DELETE']

(this prints the .pattern of the compiled regex plus the options stored
under that key)

The result is that we sometimes get an error message "Method not
allowed" for a call to PUT (or GET) on a path that should allow this method.

A simple test that bypasses the regex cache (by clearing it between
invocations) shows that compiled regular expression objects should not
be used as keys in a dictionary (at least not in Python2):

>>> import re
>>> r1 = re.compile ('a')
>>> re.purge ()
>>> r2 = re.compile ('a')
>>> r1 == r2
False
>>> d = dict (r1 = r1, r2 = r2)
>>> d
{'r1': <_sre.SRE_Pattern object at 0x7f4a0aa19d78>, 'r2':
<_sre.SRE_Pattern object at 0x7f4a0aa19e00>}

Thanks to Robert Klonner for debugging it so far that I could make this
bug-report. We're working on a fix, too, so no need to look into this
too soon.

----------
assignee: schlatterbeck
messages: 6590
nosy: schlatterbeck
severity: normal
status: new
title: REST-API: Regular expressions used as keys in dictionary

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