Pandas Full build immediately starts every time setup.py is run, even with --help

I'm running into a strange problem where a full pandas build starts every time setup.py is invoked, with any arguments whatsover: python setup.py, python setup.py --help, python setup.py xyz ... Even python -c 'import setup' starts a build.

Tested with Python 3.5 & pandas 0.18.1 on Mac OS X and Ubuntu Server.

~ $ cd /tmp

/tmp $ virtualenv -p $(which python3) env

Running virtualenv with interpreter /usr/local/bin/python3
Using base prefix '/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5'
New python executable in /private/tmp/env/bin/python3.5
Also creating executable in /private/tmp/env/bin/python
Installing setuptools, pip, wheel...done.

/tmp $ . env/bin/activate

(env) /tmp $ wget https://pypi.python.org/packages/11/09/e66eb844daba8680ddff26335d5b4fead77f60f957678243549a8dd4830d/pandas-0.18.1.tar.gz#md5=42b9dba111a8f916352f49b512c029aa

--2016-07-22 11:44:49--  https://pypi.python.org/packages/11/09/e66eb844daba8680ddff26335d5b4fead77f60f957678243549a8dd4830d/pandas-0.18.1.tar.gz
Resolving pypi.python.org... 151.101.12.223, 2a04:4e42:3::223
Connecting to pypi.python.org|151.101.12.223|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 7283184 (6.9M) [application/octet-stream]
Saving to: 'pandas-0.18.1.tar.gz'

pandas-0.18.1.tar.gz                                                100%[===================================================================================================================================================================>]   6.95M  2.10MB/s    in 3.3s

2016-07-22 11:44:52 (2.09 MB/s) - 'pandas-0.18.1.tar.gz' saved [7283184/7283184]

(env) /tmp $ tar zxf pandas-0.18.1.tar.gz

(env) /tmp $ cd pandas-0.18.1/

(env) /tmp/pandas-0.18.1 $ python setup.py --help

Running from numpy source directory.
/var/folders/84/6bwfrc955bdcvlgnhx2zqwzh0000gn/T/easy_install-f5yrgkx8/numpy-1.11.1/setup.py:327: UserWarning: Unrecognized setuptools command, proceeding with generating Cython sources and expanding templates
  warnings.warn("Unrecognized setuptools command, proceeding with "
non-existing path in 'numpy/distutils': 'site.cfg'
/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/distutils/dist.py:261: UserWarning: Unknown distribution option: 'define_macros'
  warnings.warn(msg)
Could not locate executable gfortran
Could not locate executable f95
Could not locate executable f90
Could not locate executable f77
Could not locate executable xlf90
Could not locate executable xlf
Could not locate executable ifort
Could not locate executable ifc
Could not locate executable g77
Could not locate executable g95
Could not locate executable pgfortran
don't know how to compile Fortran code on platform 'posix'
_configtest.c:1:5: warning: incompatible redeclaration of library function 'exp' [-Wincompatible-library-redeclaration]
int exp (void);
    ^
_configtest.c:1:5: note: 'exp' is a builtin with type 'double (double)'

... and so on ...

Comment From: jreback

you don't have numpy installed which is a dev requirement

Comment From: vitawasalreadytaken

Okay, this doesn't happen when numpy is installed first. But shouldn't setup.py raise an exception or warn you when numpy is missing, instead of starting the build every time it's touched?