Description:
The "lxc" package uses a bad Python package name, which starts with an underscore, making it deviate from other packages names with regards to the format. Though this worked fine in the past, now pip (starting from 8.1.2) got stricter with package names, to enhance security, and disallows that kind of format. The solution is probably just making the Python package name spell as "lxc" itself, without the underscore; however, if there's a naming conflict of some sort, it could be something like "liblxc".


Additional info:
* package version(s)
1:2.0.1-1
* config and/or log files etc.
Exception:
Traceback (most recent call last):
File "/usr/lib/python3.5/site-packages/pip/_vendor/packaging/requirements.py", line 92, in __init__
req = REQUIREMENT.parseString(requirement_string)
File "/usr/lib/python3.5/site-packages/pip/_vendor/pyparsing.py", line 1172, in parseString
raise exc
File "/usr/lib/python3.5/site-packages/pip/_vendor/pyparsing.py", line 1162, in parseString
loc, tokens = self._parse( instring, 0 )
File "/usr/lib/python3.5/site-packages/pip/_vendor/pyparsing.py", line 1028, in _parseNoCache
loc,tokens = self.parseImpl( instring, preloc, doActions )
File "/usr/lib/python3.5/site-packages/pip/_vendor/pyparsing.py", line 2462, in parseImpl
loc, exprtokens = e._parse( instring, loc, doActions )
File "/usr/lib/python3.5/site-packages/pip/_vendor/pyparsing.py", line 1028, in _parseNoCache
loc,tokens = self.parseImpl( instring, preloc, doActions )
File "/usr/lib/python3.5/site-packages/pip/_vendor/pyparsing.py", line 2719, in parseImpl
return self.expr._parse( instring, loc, doActions, callPreParse=False )
File "/usr/lib/python3.5/site-packages/pip/_vendor/pyparsing.py", line 1028, in _parseNoCache
loc,tokens = self.parseImpl( instring, preloc, doActions )
File "/usr/lib/python3.5/site-packages/pip/_vendor/pyparsing.py", line 2445, in parseImpl
loc, resultlist = self.exprs[0]._parse( instring, loc, doActions, callPreParse=False )
File "/usr/lib/python3.5/site-packages/pip/_vendor/pyparsing.py", line 1032, in _parseNoCache
loc,tokens = self.parseImpl( instring, preloc, doActions )
File "/usr/lib/python3.5/site-packages/pip/_vendor/pyparsing.py", line 1823, in parseImpl
raise ParseException(instring, loc, self.errmsg, self)
pip._vendor.pyparsing.ParseException: Expected W:(abcd...) (at char 0), (line:1, col:1)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/usr/lib/python3.5/site-packages/pip/_vendor/pkg_resources/__init__.py", line 2788, in __init__
super(Requirement, self).__init__(requirement_string)
File "/usr/lib/python3.5/site-packages/pip/_vendor/packaging/requirements.py", line 96, in __init__
requirement_string[e.loc:e.loc + 8]))
pip._vendor.packaging.requirements.InvalidRequirement: Invalid requirement, parse error at "'-lxc==0.'"

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/usr/lib/python3.5/site-packages/pip/basecommand.py", line 215, in main
status = self.run(options, args)
File "/usr/lib/python3.5/site-packages/pip/commands/freeze.py", line 85, in run
for line in freeze(**freeze_kwargs):
File "/usr/lib/python3.5/site-packages/pip/operations/freeze.py", line 47, in freeze
dependency_links
File "/usr/lib/python3.5/site-packages/pip/__init__.py", line 264, in from_dist
req = dist.as_requirement()
File "/usr/lib/python3.5/site-packages/pip/_vendor/pkg_resources/__init__.py", line 2562, in as_requirement
return Requirement.parse(spec)
File "/usr/lib/python3.5/site-packages/pip/_vendor/pkg_resources/__init__.py", line 2833, in parse
req, = parse_requirements(s)
File "/usr/lib/python3.5/site-packages/pip/_vendor/pkg_resources/__init__.py", line 2781, in parse_requirements
yield Requirement(line)
File "/usr/lib/python3.5/site-packages/pip/_vendor/pkg_resources/__init__.py", line 2790, in __init__
raise RequirementParseError(str(e))
pip._vendor.pkg_resources.RequirementParseError: Invalid requirement, parse error at "'-lxc==0.'"


Steps to reproduce:
1. Install pip 8.1.2 (if you don't already have it)
2. Install lxc
3. Run "pip freeze"