title: Numpy package installed twice in single Anaconda environment
body: <p>I just used <code>pip</code> to install <a href="https://pypi.org/project/silx/" rel="nofollow noreferrer">Silx</a> in an existing Anaconda environment (called <code>gssw</code>). Pip then started to install Numpy (one of the dependencies of Silx) even though my environment already contained an older version of Numpy that was installed as a regular conda package. To my understanding this should not happen!</p>
  
  <p>I now have two numpy packages in my enviromnent.</p>
  
  <pre><code>(gssw) C:\&gt;conda list numpy
  # packages in environment at C:\Anaconda\envs\gssw:
  #
  numpy                     1.11.2                   py35_0
  numpy                     1.15.0                    &lt;pip&gt;
  </code></pre>
  
  <p>When start Python it seems to use the latter.</p>
  
  <pre><code>(gssw) C:\&gt;python -c "import numpy; print(numpy.__version__)"
  1.15.0
  </code></pre>
  
  <p>Here is my conda info</p>
  
  <pre><code>(gssw) C:\&gt;conda info
  Current conda install:
  
                 platform : win-64
            conda version : 4.3.30
         conda is private : False
        conda-env version : 4.3.30
      conda-build version : 1.11.0
           python version : 2.7.9.final.0
         requests version : 2.12.4
         root environment : C:\Anaconda  (writable)
      default environment : C:\Anaconda\envs\gssw
         envs directories : C:\Anaconda\envs
                            C:\Users\kenter\AppData\Local\conda\conda\envs
                            C:\Users\kenter\.conda\envs
            package cache : C:\Anaconda\pkgs
                            C:\Users\kenter\AppData\Local\conda\conda\pkgs
             channel URLs : https://repo.continuum.io/pkgs/main/win-64
                            https://repo.continuum.io/pkgs/main/noarch
                            https://repo.continuum.io/pkgs/free/win-64
                            https://repo.continuum.io/pkgs/free/noarch
                            https://repo.continuum.io/pkgs/r/win-64
                            https://repo.continuum.io/pkgs/r/noarch
                            https://repo.continuum.io/pkgs/pro/win-64
                            https://repo.continuum.io/pkgs/pro/noarch
                            https://repo.continuum.io/pkgs/msys2/win-64
                            https://repo.continuum.io/pkgs/msys2/noarch
              config file : None
               netrc file : None
             offline mode : False
               user-agent : conda/4.3.30 requests/2.12.4 CPython/2.7.9 Windows/7 Windows/6.1.7601
            administrator : False
  </code></pre>
  
  <p>So my questions are...</p>
  
  <ol>
  <li><p>I assumed that it is impossible to have two packages with the same
  name in one enviroment. Is that correct or do I misunderstand how Anaconda works?</p></li>
  <li><p>What went wrong here? </p></li>
  <li><p>How to fix it?</p></li>
  </ol>
  
  <p>Please let me know if you need anymore info.</p>