"pip install regex" without "--pre" option doesn't install the newest version

It seems that "pip install regex" without "--pre" option doesn't install the 
newest version because "2013-12-31" isn't a strict version.

What steps will reproduce the problem?

$ pip uninstall regex
(snip)
$ pip install regex
(snip)
Successfully installed regex
Cleaning up...
$ pip show regex

---
Name: regex
Version: 0.1.20130125
Location: /home/msmhrt/mypython/3.3.3/lib/python3.3/site-packages
Requires:
$ pip list --outdated
$ pip list --outdated --pre
regex (Current: 0.1.20130125 Latest: 2013-12-31)
$ pip install --pre -U regex
(snip)
Successfully installed regex
Cleaning up...
$ pip show regex

---
Name: regex
Version: 2013-12-31
Location: /home/msmhrt/mypython/3.3.3.lib/python3.3/site-packages
Requires:
$

What is the expected output? What do you see instead?

$ pip list --outdated
regex (Current: 0.1.20130125 Latest: 0.1.20131231)

What version of the product are you using? On what operating system?
OS: Ubuntu 12.04 (64-bit)
Python: 3.3.3

$ pip list
pip (1.5)
regex (2013-12-31)
setuptools (2.0.2)

Please provide any additional information below.

$ python3
Python 3.3.3 (default, Dec  3 2013, 20:08:06)
[GCC 4.6.3] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from distutils.version import StrictVersion
>>> StrictVersion("0.1.20130125")
StrictVersion ('0.1.20130125')
>>> StrictVersion("2013-12-31")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/python/local/3.3.3mg/lib/python3.3/distutils/version.py", line 40, in __init__
    self.parse(vstring)
  File "/home/python/local/3.3.3mg/lib/python3.3/distutils/version.py", line 143, in parse
    raise ValueError("invalid version number '%s'" % vstring)
ValueError: invalid version number '2013-12-31'
>>>

Original issue reported on code.google.com by msm...@gmail.com on 4 Jan 2014 at 12:11

Forever-Young / mrab-regex-hg

"pip install regex" without "--pre" option doesn't install the newest version #103