clang error: unknown argument: '-mno-fused-madd' (python package installation failure)

Question

I get the following error when attempting to install psycopg2 via pip on Mavericks 10.9:

clang: error: unknown argument: \'-mno-fused-madd\' [-W         


        

Answer 1

You can tell clang to not raise this as an error by setting the following environment variables prior compilation:

export CFLAGS=-Qunused-arguments
export CPPFLAGS=-Qunused-arguments

Then pip install psycopg2should work.

I had the same when trying to pip install lxml.

Edit: if you are installing as superuser (which will likely be the case if you are trying to append to /Library/Python/2.7/site-packages, the native Apple factory-installed Python distribution which ships with OS X, rather than to some other Python distribution which you have subsequently installed yourself), then you will need to do, as described by @Thijs Kuipers in comments below:

sudo -E pip install psycopg2

or the equivalent, for whatever other package name you may be substituting in place of psycopg2.

UPDATE [2014-05-16]: Apple has fixed this problem with updated system Pythons (2.7, 2.6, and 2.5) in OS X 10.9.3 so the workaround is no longer necessary when using the latest Mavericks and Xcode 5.1+. However, as of now, the workaround is still required for OS X 10.8.x (Mountain Lion, currently 10.8.5) if you are using Xcode 5.1+ there.