clang: error: unknown argument: '-mno-fused-madd' [-Wunused-command-line-argument-hard-error-in-future]

Question

I get the following error trying to install Scrapy in a Mavericks OS.

I have command line tools and X11 installed I don't really know whats going on and I haven`t found the same error browsing through the Web. I think it might be related to some change in Xcode 5.1

Thanks for the answers!

this is part of the command output:

$pip install scrapy

---

.
.
.
.

Downloading/unpacking cryptography>=0.2.1 (from pyOpenSSL->scrapy)
  Downloading cryptography-0.3.tar.gz (208kB): 208kB downloaded
  Running setup.py egg_info for package cryptography
    OS/X: confusion between 'cc' versus 'gcc' (see issue 123)
    will not use '__thread' in the C code
    clang: error: unknown argument: '-mno-fused-madd' [-Wunused-command-line-argument-hard-error-in-future]
    clang: note: this will be a hard error (cannot be downgraded to a warning) in the future
    Traceback (most recent call last):
      File "<string>", line 16, in <module>
      File "/Users/agonzamart/.virtualenvs/Parser/build/cryptography/setup.py", line 156, in <module>
        "test": PyTest,
      File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/distutils/core.py", line 112, in setup
        _setup_distribution = dist = klass(attrs)
      File "/Users/agonzamart/.virtualenvs/Parser/lib/python2.7/site-packages/setuptools/dist.py", line 265, in __init__
        self.fetch_build_eggs(attrs.pop('setup_requires'))
      File "/Users/agonzamart/.virtualenvs/Parser/lib/python2.7/site-packages/setuptools/dist.py", line 289, in fetch_build_eggs
        parse_requirements(requires), installer=self.fetch_build_egg
      File "/Users/agonzamart/.virtualenvs/Parser/lib/python2.7/site-packages/pkg_resources.py", line 618, in resolve
        dist = best[req.key] = env.best_match(req, self, installer)
      File "/Users/agonzamart/.virtualenvs/Parser/lib/python2.7/site-packages/pkg_resources.py", line 862, in best_match
        return self.obtain(req, installer) # try and download/install
      File "/Users/agonzamart/.virtualenvs/Parser/lib/python2.7/site-packages/pkg_resources.py", line 874, in obtain
        return installer(requirement)
      File "/Users/agonzamart/.virtualenvs/Parser/lib/python2.7/site-packages/setuptools/dist.py", line 339, in fetch_build_egg
        return cmd.easy_install(req)
      File "/Users/agonzamart/.virtualenvs/Parser/lib/python2.7/site-packages/setuptools/command/easy_install.py", line 623, in easy_install
        return self.install_item(spec, dist.location, tmpdir, deps)
      File "/Users/agonzamart/.virtualenvs/Parser/lib/python2.7/site-packages/setuptools/command/easy_install.py", line 653, in install_item
        dists = self.install_eggs(spec, download, tmpdir)
      File "/Users/agonzamart/.virtualenvs/Parser/lib/python2.7/site-packages/setuptools/command/easy_install.py", line 849, in install_eggs
        return self.build_and_install(setup_script, setup_base)
      File "/Users/agonzamart/.virtualenvs/Parser/lib/python2.7/site-packages/setuptools/command/easy_install.py", line 1130, in build_and_install
        self.run_setup(setup_script, setup_base, args)
      File "/Users/agonzamart/.virtualenvs/Parser/lib/python2.7/site-packages/setuptools/command/easy_install.py", line 1118, in run_setup
        raise DistutilsError("Setup script exited with %s" % (v.args[0],))
    distutils.errors.DistutilsError: Setup script exited with error: command 'cc' failed with exit status 1
    Complete output from command python setup.py egg_info:
    OS/X: confusion between 'cc' versus 'gcc' (see issue 123)

will not use '__thread' in the C code

clang: error: unknown argument: '-mno-fused-madd' [-Wunused-command-line-argument-hard-error-in-future]

clang: note: this will be a hard error (cannot be downgraded to a warning) in the future

Traceback (most recent call last):

  File "<string>", line 16, in <module>

  File "/Users/agonzamart/.virtualenvs/Parser/build/cryptography/setup.py", line 156, in <module>

    "test": PyTest,

  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/distutils/core.py", line 112, in setup

    _setup_distribution = dist = klass(attrs)

  File "/Users/agonzamart/.virtualenvs/Parser/lib/python2.7/site-packages/setuptools/dist.py", line 265, in __init__

    self.fetch_build_eggs(attrs.pop('setup_requires'))

  File "/Users/agonzamart/.virtualenvs/Parser/lib/python2.7/site-packages/setuptools/dist.py", line 289, in fetch_build_eggs

    parse_requirements(requires), installer=self.fetch_build_egg

  File "/Users/agonzamart/.virtualenvs/Parser/lib/python2.7/site-packages/pkg_resources.py", line 618, in resolve

    dist = best[req.key] = env.best_match(req, self, installer)

  File "/Users/agonzamart/.virtualenvs/Parser/lib/python2.7/site-packages/pkg_resources.py", line 862, in best_match

    return self.obtain(req, installer) # try and download/install

  File "/Users/agonzamart/.virtualenvs/Parser/lib/python2.7/site-packages/pkg_resources.py", line 874, in obtain

    return installer(requirement)

  File "/Users/agonzamart/.virtualenvs/Parser/lib/python2.7/site-packages/setuptools/dist.py", line 339, in fetch_build_egg

    return cmd.easy_install(req)

  File "/Users/agonzamart/.virtualenvs/Parser/lib/python2.7/site-packages/setuptools/command/easy_install.py", line 623, in easy_install

    return self.install_item(spec, dist.location, tmpdir, deps)

  File "/Users/agonzamart/.virtualenvs/Parser/lib/python2.7/site-packages/setuptools/command/easy_install.py", line 653, in install_item

    dists = self.install_eggs(spec, download, tmpdir)

  File "/Users/agonzamart/.virtualenvs/Parser/lib/python2.7/site-packages/setuptools/command/easy_install.py", line 849, in install_eggs

    return self.build_and_install(setup_script, setup_base)

  File "/Users/agonzamart/.virtualenvs/Parser/lib/python2.7/site-packages/setuptools/command/easy_install.py", line 1130, in build_and_install

    self.run_setup(setup_script, setup_base, args)

  File "/Users/agonzamart/.virtualenvs/Parser/lib/python2.7/site-packages/setuptools/command/easy_install.py", line 1118, in run_setup

    raise DistutilsError("Setup script exited with %s" % (v.args[0],))

distutils.errors.DistutilsError: Setup script exited with error: command 'cc' failed with exit status 1

----------------------------------------
Cleaning up...
Command python setup.py egg_info failed with error code 1 in /Users/agonzamart/.virtualenvs/Parser/build/cryptography

---

Answer 1

It is due to a change in clang defaults in Xcode 5.1 and Apple not noticing that it would break extension module builds using the system Python. One workaround is to define the following environment variables first:

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

UPDATE [2014-05-16]: As expected, 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.