check-pip-dependencies

A script that does the same as pip install --no-install but also highlights dependency conflict issues currently not otherwise caught.

The Problem

pip doesn't currently catch some obvious dependency issues, due to its 'whichever comes first' dependency downloading.

Consider the following example requirements.txt file, on a computer that already has python-dateutil version 1.4.1 installed:

python-dateutil
django-tastypie
django-app-1
django-app-2

Note these packages have the following dependencies:

• django-tastypie requires python-dateutil >= 1.5, != 2.0
• django-app-1 requires Django >= 1.4
• django-app-2 requires Django >= 1.3, < 1.5

If you were to simply run pip install -r requirements.txt then the following would be installed/ not touched:

python-dateutil==1.4.1
django-tastypie==0.10.0
django-app-1==1.0.0
django-app-2==1.0.0
Django==1.5.2

Which conflicts both in django-tastypie (incompatible python-dateutil version) and django-app-2 (incompatible Django version).

The Solution

This script should be run in a virtualenv, providing a requirements file as the only argument. It outputs any conflicts that it finds; its output on the above requirements.txt file (wrapped for clarity) is:

(test)$ python check-pip-dependencies.py requirements.txt
python-dateutil>=1.5,!=2.0 (from django-tastypie->-r requirements.txt (line 2))
    conflicts with installed python-dateutil 1.4.1
django>=1.3,<1.5 (from django-app-2->-r requirements.txt (line 4)),
    but pip will install version 1.5.2 from Django>=1.4
    (from django-app-1->-r requirements.txt (line 3))

You can then adjust your requirements.txt file to work around these issues (in this case, you could specify the version of python-dateutil to match django-tastypie, and specify a Django version that fits, presumably 1.4.x).

Note that as this basically performs a pip install --no-install -r <file>, a further pip install -r <file> will not have to redownload the packages.

There is a --verbose option to output the packages being downloaded (but not installed) by pip as it goes.