Installing a quite normal Django stack on windows with postgres support yields a lot of questions on StackOverflow; especially the installation of psycopg2 can be a bit tricky. The typical error message you will receive is: Unable to find vcvarsall.bat. This message appears when a Python package contains the source code for a native extension module (.pyd), but does not have a pre-built copy of the module.
In this blog post I’ll document the easiest way with Python2.7 and the Microsoft Visual C++ Compiler for Python 2.7 which doesn’t involve installing the full Visual Studio suite. This will come in handy when using it to build a self containing CI setup that can update to the latest psycopg2 by compiling the C extension yourself when needed.
Step 1: Install Python2.7
I used the 64-bit MSI installer from https://www.python.org/downloads/release/python-2710/. You can use the installer to add Python to your Path or do it by hand:
Step 2: Install virtualenv
Install virtualenv and some tools to ease the creation of virtual python environments
cmd pip install virtualenv pip install virtualenvwrapper-win mkvirtualenv test
Step 3: Download and install postgres
Before you continue to install python packages inside you virtualenvs download postgres itself. It contains files that are needed when compiling the psycopg2 python package. Just use the last 64 bit installer from http://www.enterprisedb.com/products-services-training/pgdownload#windows
Important: add the postgres C:\Program Files\PostgreSQL\9.4\bin folder to your path. It contains the .dll needed for psycopg2.
Step 4: Install Microsoft Visual C++ Compiler for Python 2.7
Download it from here: http://www.microsoft.com/en-us/download/details.aspx?id=44266 and run the installer.
You can now proceed installing other packages, assuming no further C extensions are listed in the requirement.txt
Step 5: Install django and psycopg2
Your system should now be ready for installing psycopg2
cmd workon test pip install django pip install psycopg2
python import psycopg2
When you get an error like this: “ImportError: DLL load failed: %1 is not a valid Win32-application” you probably havn’t configure the postgres bin folder in your environments path.