Freeze a requirements.txt based on what's currently installed
pip install freezeray
Freezeray takes an existing requirements.txt file you have and writes a new file with the currently installed versions of all the packages in your input file plus their dependencies.
It's basically pip freeze for a subset of the packages you have installed at any given time.
The command line tool reads in an input requirements.txt file and writes to a separate output file. Once you've installed, it's as easy as running this:
freezeray <path to input file> <path to output file>