pip fails to install packages from requirements.txt

It looks like the numexpr package has an install-time dependency on numpy. Pip makes two passes through your requirements: first it downloads all packages and runs each one’s setup.py to get its metadata, and then it installs them all in a second pass.

So, numexpr is trying to import from numpy in its setup.py, but when pip first runs numexpr’s setup.py, it has not yet installed numpy.

This is also why you don’t see this error when you install the packages one by one: if you install them one at a time, numpy will be fully installed in your environment before you pip install numexpr.

The only solution is to install pip install numpy before you ever run pip install -r requirements.txt — you won’t be able to do this in a single command with a single requirements.txt file.

More info here: https://github.com/pypa/pip/issues/25

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