title: Installing requirements.txt into virtual environment
body: <p>I have a directory with scripts *.py that I need to compile on another computer that includes different versions of modules. I opened the terminal in that directory and have created requirements:</p>
  <pre><code>pip freeze &gt; requirements.txt 
  </code></pre>
  <p>Then I created a vertual environment and tried to installed packages from requirements.txt</p>
  <pre><code>virtualenv compilation
  source compilation/bin/activate
  python3.6 -m pip install -r requirements.txt
  </code></pre>
  <p>It ended with this:</p>
  <pre><code>ERROR: Cannot install babel==2.7.0, gitsome==0.8.4 and pytz==2021.1 because these package versions have conflicting dependencies.
  
  The conflict is caused by:
      The user requested pytz==2021.1
      babel 2.7.0 depends on pytz&gt;=2015.7
      gitsome 0.8.4 depends on pytz&lt;2017.0 and &gt;=2016.3
  
  To fix this you could try to:
  1. loosen the range of package versions you've specified
  2. remove package versions to allow pip attempt to solve the dependency conflict
  
  ERROR: ResolutionImpossible: for help visit https://pip.pypa.io/en/latest/user_guide/#fixing-conflicting-dependencies
  </code></pre>
  <p>Why is there a conflict when these packages work in non-virtual python3.6, please? What to do with that, please?</p>
  <p><strong>After babel and gitsome upgrade</strong></p>
  <pre><code>ERROR: Cannot install babel==2.7.0, gitsome==0.8.4, pandas==1.1.5 and pytz==2016.10 because these package versions have conflicting dependencies.
  
  The conflict is caused by:
      The user requested pytz==2016.10
      babel 2.7.0 depends on pytz&gt;=2015.7
      gitsome 0.8.4 depends on pytz&lt;2017.0 and &gt;=2016.3
      pandas 1.1.5 depends on pytz&gt;=2017.2
  
  To fix this you could try to:
  1. loosen the range of package versions you've specified
  2. remove package versions to allow pip attempt to solve the dependency conflict
  
  ERROR: ResolutionImpossible: for help visit https://pip.pypa.io/en/latest/user_guide/#fixing-conflicting-dependencies
  </code></pre>
  <p><strong>Downgrading pytz</strong></p>
  <pre><code>ERROR: pip's dependency resolver does not currently take into account all the packages that are installed. This behaviour is the source of the following dependency conflicts.
  pandas 1.1.5 requires pytz&gt;=2017.2, but you have pytz 2015.7 which is incompatible.
  gitsome 0.8.4 requires pytz&lt;2017.0,&gt;=2016.3, but you have pytz 2015.7 which is incompatible.
  Successfully installed pytz-2016.10
  Removed build tracker: '/tmp/pip-req-tracker-8c5_ezeo'
  </code></pre>