title: pip install packages failing: Invalid requirement & No matching distribution
body: <p>I am trying to install packages in a python 3.6.3 virtual environment. I keep getting errors.</p>
  
  <p>I have tried pip with <code>--ignore-installed</code> flag like: <code>pip install -I -r package-list.txt</code>. </p>
  
  <p>Here is part of what I have in <code>package-list.txt</code>.</p>
  
  <pre><code># This file may be used to create an environment using:
  # $ conda create --name &lt;env&gt; --file &lt;this file&gt;
  # platform: linux-64
  _libgcc_mutex==0.1==main
  appdirs==1.4.3==pypi_0
  asn1crypto==0.24.0==py36_0
  beautifulsoup4==4.7.1==py36_1
  blas==1.0==mkl
  bzip2==1.0.6==h14c3975_5
  ca-certificates==2019.6.16==hecc5488_0
  cairo==1.14.12==h8948797_3
  certifi==2019.6.16==py36_1
  cffi==1.12.1==py36h2e261b9_0
  chardet==3.0.4==py36_1
  cloudpickle==0.8.0==pypi_0
  cryptography==2.5==py36h1ba5d50_0
  cycler==0.10.0==pypi_0
  dask==1.1.4==pypi_0
  decorator==4.4.0==pypi_0
  ffmpeg==4.0==hcdf2ecd_0
  fontconfig==2.13.0==h9420a91_0
  freeglut==3.0.0==hf484d3e_5
  freetype==2.9.1==h8a8886c_1
  fuzzywuzzy==0.17.0==py_0
  glib==2.56.2==hd408876_0
  graphite2==1.3.13==h23475e2_0
  harfbuzz==1.8.8==hffaf4a1_0
  hdf5==1.10.2==hba1933b_1
  icu==58.2==h9c2bf20_1
  idna==2.8==py36_0
  intel-openmp==2019.3==199
  jasper==2.0.14==h07fcdf6_1
  jpeg==9b==h024ee3a_2
  kiwisolver==1.0.1==pypi_0
  libedit==3.1.20181209==hc058e9b_0
  libffi==3.2.1==hd88cf55_4
  libgcc-ng==8.2.0==hdf63c60_1
  libgfortran-ng==7.3.0==hdf63c60_0
  libglu==9.0.0==hf484d3e_1
  ...
  </code></pre>
  
  <p>With first package <code>_libgcc_mutex==0.1==main</code> I get this error:</p>
  
  <pre><code>Ignoring pip: markers 'python_version &lt; "3"' don't match your environment
  ERROR: Invalid requirement: '_libgcc_mutex==0.1==main' (from line 4 of package-list3.txt)
  </code></pre>
  
  <p>Without <code>_libgcc_mutex==0.1==main</code> I get:</p>
  
  <pre><code>Ignoring pip: markers 'python_version &lt; "3"' don't match your environment
  Looking in links: /cvmfs/soft.computecanada.ca/custom/python/wheelhouse/avx2, /cvmfs/soft.computecanada.ca/custom/python/wheelhouse/generic
  Collecting appdirs==1.4.3==pypi_0 (from -r package-list2.txt (line 4))
    ERROR: Could not find a version that satisfies the requirement appdirs==1.4.3==pypi_0 (from -r package-list2.txt (line 4)) (from versions: 1.1.0, 1.2.0, 1.3.0, 1.4.0, 1.4.1, 1.4.2, 1.4.3)
  ERROR: No matching distribution found for appdirs==1.4.3==pypi_0 (from -r package-list2.txt (line 4))
  </code></pre>