virtualEnvironment/lib/python2.7/site-packages/setuptools/command/easy_install.py
def check_site_dir(self):
        """Verify that self.install_dir is .pth-capable dir, if needed"""

        instdir = normalize_path(self.install_dir)
        pth_file = os.path.join(instdir, 'easy-install.pth')

        # Is it a configured, PYTHONPATH, implicit, or explicit site dir?
        is_site_dir = instdir in self.all_site_dirs

        if not is_site_dir and not self.multi_version:
            # No?  Then directly test whether it does .pth file processing
            is_site_dir = self.check_pth_processing()
        else:
            # make sure we can write to target dir
            testfile = self.pseudo_tempname() + '.write-test'
            test_exists = os.path.exists(testfile)
            try:
                if test_exists:
                    os.unlink(testfile)
                open(testfile, 'w').close()
                os.unlink(testfile)
            except (OSError, IOError):
                self.cant_write_to_target()

        if not is_site_dir and not self.multi_version:
            # Can't install non-multi to non-site dir
            raise DistutilsError(self.no_default_version_msg())

        if is_site_dir:
            if self.pth_file is None:
                self.pth_file = PthDistributions(pth_file, self.all_site_dirs)
        else:
            self.pth_file = None

        PYTHONPATH = os.environ.get('PYTHONPATH', '').split(os.pathsep)
        if instdir not in map(normalize_path, [_f for _f in PYTHONPATH if _f]):
            # only PYTHONPATH dirs need a site.py, so pretend it's there
            self.sitepy_installed = True
        elif self.multi_version and not os.path.exists(pth_file):
            self.sitepy_installed = True  # don't need site.py in this case
            self.pth_file = None  # and don't create a .pth file
        self.install_dir = instdir
def check_site_dir(self):
        """Verify that self.install_dir is .pth-capable dir, if needed"""

        instdir = normalize_path(self.install_dir)
        pth_file = os.path.join(instdir, 'easy-install.pth')

        # Is it a configured, PYTHONPATH, implicit, or explicit site dir?
        is_site_dir = instdir in self.all_site_dirs

        if not is_site_dir and not self.multi_version:
            # No?  Then directly test whether it does .pth file processing
            is_site_dir = self.check_pth_processing()
        else:
            # make sure we can write to target dir
            testfile = self.pseudo_tempname() + '.write-test'
            test_exists = os.path.exists(testfile)
            try:
                if test_exists:
                    os.unlink(testfile)
                open(testfile, 'w').close()
                os.unlink(testfile)
            except (OSError, IOError):
                self.cant_write_to_target()

        if not is_site_dir and not self.multi_version:
            # Can't install non-multi to non-site dir
            raise DistutilsError(self.no_default_version_msg())

        if is_site_dir:
            if self.pth_file is None:
                self.pth_file = PthDistributions(pth_file, self.all_site_dirs)
        else:
            self.pth_file = None

        PYTHONPATH = os.environ.get('PYTHONPATH', '').split(os.pathsep)
        if instdir not in map(normalize_path, [_f for _f in PYTHONPATH if _f]):
            # only PYTHONPATH dirs need a site.py, so pretend it's there
            self.sitepy_installed = True
        elif self.multi_version and not os.path.exists(pth_file):
            self.sitepy_installed = True  # don't need site.py in this case
            self.pth_file = None  # and don't create a .pth file
        self.install_dir = instdir
Verify that self.install_dir is .pth-capable dir, if needed