title: Getting error while using pip installation
body: <p>I am trying to install <a href="https://github.com/gunthercox/ChatterBot" rel="nofollow noreferrer">Chatterbot</a> using pip but getting following error.</p>
  
  <blockquote>
    <p>Command "python setup.py egg_info" failed with error code 1 in
    /private/var/folders/nw/vxggqrcx463g3f3zxp71dc5r0000gn/T/pip-build-8wG6yW/ruamel.yaml/</p>
  </blockquote>
  
  <p>Full log is as below</p>
  
  <pre><code>➜  Documents pip install ./ChatterBot
  Processing ./ChatterBot
  Collecting chatterbot-corpus&lt;1.1,&gt;=1.0 (from ChatterBot==0.7.3)
    Using cached chatterbot_corpus-1.0.0-py2.py3-none-any.whl
  Collecting jsondatabase&lt;1.0.0,&gt;=0.1.7 (from ChatterBot==0.7.3)
    Using cached jsondatabase-0.1.7-py2.py3-none-any.whl
  Collecting nltk&lt;4.0,&gt;=3.2 (from ChatterBot==0.7.3)
    Using cached nltk-3.2.4.tar.gz
  Collecting pymongo&lt;4.0,&gt;=3.3 (from ChatterBot==0.7.3)
    Using cached pymongo-3.4.0-cp27-cp27m-macosx_10_12_intel.whl
  Collecting python-dateutil&lt;2.7,&gt;=2.6 (from ChatterBot==0.7.3)
    Using cached python_dateutil-2.6.1-py2.py3-none-any.whl
  Collecting python-twitter&lt;4.0,&gt;=3.0 (from ChatterBot==0.7.3)
    Using cached python_twitter-3.3-py2-none-any.whl
  Collecting sqlalchemy&lt;1.2,&gt;=1.1 (from ChatterBot==0.7.3)
    Using cached SQLAlchemy-1.1.11.tar.gz
  Collecting ruamel.yaml&lt;=0.15 (from chatterbot-corpus&lt;1.1,&gt;=1.0-&gt;ChatterBot==0.7.3)
    Using cached ruamel.yaml-0.15.0.tar.gz
      Complete output from command python setup.py egg_info:
      /var/folders/nw/vxggqrcx463g3f3zxp71dc5r0000gn/T/tmp_ruamel_H5mSkZ/test_ruamel_yaml.c:6:8: warning: explicitly assigning value of variable of type 'yaml_parser_t' (aka 'struct yaml_parser_s') to itself [-Wself-assign]
      parser = parser;  /* prevent warning */
      ~~~~~~ ^ ~~~~~~
      /var/folders/nw/vxggqrcx463g3f3zxp71dc5r0000gn/T/tmp_ruamel_H5mSkZ/test_ruamel_yaml.c:6:10: warning: variable 'parser' is uninitialized when used here [-Wuninitialized]
      parser = parser;  /* prevent warning */
               ^~~~~~
      /var/folders/nw/vxggqrcx463g3f3zxp71dc5r0000gn/T/tmp_ruamel_H5mSkZ/test_ruamel_yaml.c:5:1: note: variable 'parser' is declared here
      yaml_parser_t parser;
      ^
      2 warnings generated.
      /var/folders/nw/vxggqrcx463g3f3zxp71dc5r0000gn/T/tmp_ruamel_H5mSkZ/test_ruamel_yaml.c:6:8: warning: explicitly assigning value of variable of type 'yaml_parser_t' (aka 'struct yaml_parser_s') to itself [-Wself-assign]
      parser = parser;  /* prevent warning */
      ~~~~~~ ^ ~~~~~~
      /var/folders/nw/vxggqrcx463g3f3zxp71dc5r0000gn/T/tmp_ruamel_H5mSkZ/test_ruamel_yaml.c:6:10: warning: variable 'parser' is uninitialized when used here [-Wuninitialized]
      parser = parser;  /* prevent warning */
               ^~~~~~
      /var/folders/nw/vxggqrcx463g3f3zxp71dc5r0000gn/T/tmp_ruamel_H5mSkZ/test_ruamel_yaml.c:5:1: note: variable 'parser' is declared here
      yaml_parser_t parser;
      ^
      2 warnings generated.
      sys.argv ['-c', 'egg_info', '--egg-base', 'pip-egg-info']
      test compiling test_ruamel_yaml
      Traceback (most recent call last):
        File "&lt;string&gt;", line 1, in &lt;module&gt;
        File "/private/var/folders/nw/vxggqrcx463g3f3zxp71dc5r0000gn/T/pip-build-8wG6yW/ruamel.yaml/setup.py", line 858, in &lt;module&gt;
          main()
        File "/private/var/folders/nw/vxggqrcx463g3f3zxp71dc5r0000gn/T/pip-build-8wG6yW/ruamel.yaml/setup.py", line 847, in main
          setup(**kw)
        File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/distutils/core.py", line 111, in setup
          _setup_distribution = dist = klass(attrs)
        File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/setuptools/dist.py", line 272, in __init__
          _Distribution.__init__(self,attrs)
        File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/distutils/dist.py", line 287, in __init__
          self.finalize_options()
        File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/setuptools/dist.py", line 326, in finalize_options
          ep.require(installer=self.fetch_build_egg)
        File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources/__init__.py", line 2385, in require
          reqs = self.dist.requires(self.extras)
        File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources/__init__.py", line 2617, in requires
          dm = self._dep_map
        File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources/__init__.py", line 2606, in _dep_map
          if invalid_marker(marker):
        File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources/__init__.py", line 1424, in is_invalid_marker
          cls.evaluate_marker(text)
        File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources/__init__.py", line 1549, in _markerlib_evaluate
          env = cls._translate_metadata2(_markerlib.default_environment())
        File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources/__init__.py", line 1537, in _translate_metadata2
          for key, value in env
        File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources/__init__.py", line 1536, in &lt;genexpr&gt;
          (key.replace('.', '_'), value)
      ValueError: too many values to unpack
  
      ----------------------------------------
  Command "python setup.py egg_info" failed with error code 1 in /private/var/folders/nw/vxggqrcx463g3f3zxp71dc5r0000gn/T/pip-build-8wG6yW/ruamel.yaml/
  </code></pre>
  
  <p>My pip installation is already at latest version. I even tried re-installing it as suggested on other websites but couldn't make it working yet. Any help is appreciated.</p>