環境

• Python 3.6.6 :: Anaconda, Inc.
• pip 18.0
• Windows10
• conda 4.5.11

問題

先日conda update --allでパッケージをアップデートしたら、pip installで次のエラーが発生しました。

>python -m pip install docutils
Exception:
Traceback (most recent call last):
  File "C:\Users\yuji3\Anaconda3_5.2.0\lib\site-packages\pip\_vendor\pkg_resources\__init__.py", line 2869, in _dep_map
    return self.__dep_map
  File "C:\Users\yuji3\Anaconda3_5.2.0\lib\site-packages\pip\_vendor\pkg_resources\__init__.py", line 2663, in __getattr__
    raise AttributeError(attr)
AttributeError: _DistInfoDistribution__dep_map

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Users\yuji3\Anaconda3_5.2.0\lib\site-packages\pip\_vendor\packaging\requirements.py", line 93, in __init__
    req = REQUIREMENT.parseString(requirement_string)
  File "C:\Users\yuji3\Anaconda3_5.2.0\lib\site-packages\pip\_vendor\pyparsing.py", line 1632, in parseString
    raise exc
  File "C:\Users\yuji3\Anaconda3_5.2.0\lib\site-packages\pip\_vendor\pyparsing.py", line 1622, in parseString
    loc, tokens = self._parse( instring, 0 )
  File "C:\Users\yuji3\Anaconda3_5.2.0\lib\site-packages\pip\_vendor\pyparsing.py", line 1379, in _parseNoCache
    loc,tokens = self.parseImpl( instring, preloc, doActions )
  File "C:\Users\yuji3\Anaconda3_5.2.0\lib\site-packages\pip\_vendor\pyparsing.py", line 3395, in parseImpl
    loc, exprtokens = e._parse( instring, loc, doActions )
  File "C:\Users\yuji3\Anaconda3_5.2.0\lib\site-packages\pip\_vendor\pyparsing.py", line 1383, in _parseNoCache
    loc,tokens = self.parseImpl( instring, preloc, doActions )
  File "C:\Users\yuji3\Anaconda3_5.2.0\lib\site-packages\pip\_vendor\pyparsing.py", line 3183, in parseImpl
    raise ParseException(instring, loc, self.errmsg, self)
pip._vendor.pyparsing.ParseException: Expected stringEnd (at char 33), (line:1, col:34)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Users\yuji3\Anaconda3_5.2.0\lib\site-packages\pip\_vendor\pkg_resources\__init__.py", line 2949, in __init__
    super(Requirement, self).__init__(requirement_string)
  File "C:\Users\yuji3\Anaconda3_5.2.0\lib\site-packages\pip\_vendor\packaging\requirements.py", line 97, in __init__
    requirement_string[e.loc:e.loc + 8]))
pip._vendor.packaging.requirements.InvalidRequirement: Invalid requirement, parse error at "'; extra '"

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Users\yuji3\Anaconda3_5.2.0\lib\site-packages\pip\_internal\basecommand.py", line 141, in main
    status = self.run(options, args)
  File "C:\Users\yuji3\Anaconda3_5.2.0\lib\site-packages\pip\_internal\commands\install.py", line 330, in run
    self._warn_about_conflicts(to_install)
  File "C:\Users\yuji3\Anaconda3_5.2.0\lib\site-packages\pip\_internal\commands\install.py", line 456, in _warn_about_conflicts
    package_set, _dep_info = check_install_conflicts(to_install)
  File "C:\Users\yuji3\Anaconda3_5.2.0\lib\site-packages\pip\_internal\operations\check.py", line 98, in check_install_conflicts
    package_set = create_package_set_from_installed()
  File "C:\Users\yuji3\Anaconda3_5.2.0\lib\site-packages\pip\_internal\operations\check.py", line 41, in create_package_set_from_installed
    package_set[name] = PackageDetails(dist.version, dist.requires())
  File "C:\Users\yuji3\Anaconda3_5.2.0\lib\site-packages\pip\_vendor\pkg_resources\__init__.py", line 2607, in requires
    dm = self._dep_map
  File "C:\Users\yuji3\Anaconda3_5.2.0\lib\site-packages\pip\_vendor\pkg_resources\__init__.py", line 2871, in _dep_map
    self.__dep_map = self._compute_dependencies()
  File "C:\Users\yuji3\Anaconda3_5.2.0\lib\site-packages\pip\_vendor\pkg_resources\__init__.py", line 2881, in _compute_dependencies
    reqs.extend(parse_requirements(req))
  File "C:\Users\yuji3\Anaconda3_5.2.0\lib\site-packages\pip\_vendor\pkg_resources\__init__.py", line 2942, in parse_requirements
    yield Requirement(line)
  File "C:\Users\yuji3\Anaconda3_5.2.0\lib\site-packages\pip\_vendor\pkg_resources\__init__.py", line 2951, in __init__
    raise RequirementParseError(str(e))
pip._vendor.pkg_resources.RequirementParseError: Invalid requirement, parse error at "'; extra '"
You are using pip version 18.0, however version 18.1 is available.
You should consider upgrading via the 'python -m pip install --upgrade pip' command.

質問

上記のエラーは、どのようにして調査・解決すればよいでしょうか？