Illegal instruction: 4 when running Django

Question

I made clean install of Django v1.11.10 now. When I run python manage.py runserver everything works fine. But when I try connect to Postgres database, I install

Answer 1

psycopg2 is partly written in C and needs to be compiled. When you pip install a package, there's often a pre-compiled binary wheel available for download.

For some reason, the pre-compiled psycopg2 module contains instructions that your CPU can't recognize (probably because your processor is too old). You can fix this by compiling the module yourself, which will ensure the code works on your CPU:

$ pip install --no-binary psycopg2 psycopg2

--no-binary psycopg2 is a separate option so you'll have to specify the package name twice. You can include this in your requirements.txt as well:

psycopg2==a.b.c    --no-binary psycopg2

Answer 2

Reinstalling with pip install --no-binary psycopg2 psycopg2 solved problem

Answer 3

Blender's answer and this other question pointed to the problem, but when running the suggested command, I was getting the following error:

 Error: pg_config executable not found.

    pg_config is required to build psycopg2 from source.  Please add the directory
    containing pg_config to the $PATH or specify the full executable path with the
    option:

        python setup.py build_ext --pg-config /path/to/pg_config build ...

    or with the pg_config option in 'setup.cfg'.

As I have no clue about settings, configurations and so on, it took a while to find out how to do it. Here it is in case somebody else faces the same issue:

pip uninstall psycopg2

then

export PATH=$PATH:/Applications/Postgres.app/Contents/Versions/latest/bin/

then

pip install --no-binary :all: psycopg2

This solved the problem for me.