How to do it...

1. Tag the in-house version of the file. Assuming you are using Git, a tag is generated by using the following:

      git tag -a <tag_name> -m "<tag_message>"
      # git tag -a v0.3 -m "Changed the calculations"

1. Upload it to the version control system.
2. Indicate the local version in the requirements.txt file, as shown in the following example:

      git+https://<vcs>/<dependency>@<tag_name>#egg=<dependency>
      # git+https://gitlab/pump_laws@v0.3#egg=pump_laws

1. Write the constraints.txt file in the same manner as a requirements.txt file. The following example comes from https://github.com/mldbai/mldb (this was released under the Apache v2.0 license by MLDB.ai):

      # math / science / graph stuff
      bokeh==0.11.1
      numpy==1.10.4
      pandas==0.17.1
      scipy==0.17.0
      openpyxl==2.3.3
      patsy==0.4.1
      matplotlib==1.5.1
      ggplot==0.6.8
      Theano==0.7.0
      seaborn==0.7.0
      scikit-learn==0.17

      pymldb==0.8.1
      pivottablejs==0.1.0

      # Progress bar
      tqdm==4.11.0

      # notebook and friends
      ipython==5.1.0
      jupyter==1.0.0
      jupyter-client==4.4.0
      jupyter-console==5.0.0
      jupyter-core==4.2.1

      # validator
      uWSGI==2.0.12
      pycrypto==2.6.1

      tornado==4.4.2

      ## The following requirements were added by pip freeze:
      backports-abc==0.5
      backports.shutil-get-terminal-size==1.0.0
      backports.ssl-match-hostname==3.5.0.1
      bleach==1.5.0

      ***further files truncated***

1. Next, run the command, pip install -c constraints.txt, to make the file available to Python.