New submission from Trevor Bekolay:

I was having an issue installing a package in Python 3, which installed 
properly in Python 2. This is the error message I got:

    Complete output from command python setup.py egg_info:
    Traceback (most recent call last):

    ... snip unhelpful traceback ...

      File 
"/usr/local/Cellar/python3/3.4.3/Frameworks/Python.framework/Versions/3.4/lib/python3.4/configparser.py",
 line 423, in _interpolate_some

        "found: %r" % (rest,))

    configparser.Interpolation

    ----------------------------------------
    Command "python setup.py egg_info" failed with error code 1 in 
/private/var/folders/12/p4ngkfbx2pnb1ln81csjb19c0000gn/T/pip-build-6xhgg5x6/nengo

This wasn't a super helpful error message. I managed to figure out that Python 
3 (or setuptools?) was attempting to parse my ~/.pypirc file, which raised a 
configparser.InterpolationSyntaxError because my password contained a 
percent-sign. Configparser doesn't try to interpolate this string in Python 2, 
so it worked fine. As a workaround, I've changed my PyPI password, but this 
failure was quite surprising to me.

As for what I would expect to happen, I would not expect interpolation to 
happen if I don't want it to happen. All of the examples shown on in the docs 
use the syntax "%(key)s" or "${key}". If this is the only way to interpolate, 
then why is "%" ambiguous? Surely we can look forward one character, and if 
it's not "(" then "%" should be interpreted literally. Instead, configparser 
requires me to disambiguate with "%%". But, this would cause my string to be 
parsed incorrectly in Python 2's configparser, so I'm unable to make that 
change.

----------
components: Library (Lib)
messages: 242283
nosy: tbekolay
priority: normal
severity: normal
status: open
title: Configparser interpolation is unexpected
type: behavior
versions: Python 3.2, Python 3.3, Python 3.4

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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue24086>
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