capybara/virtualenv/lib/python2.7/site-packages/pip/index.py
def _link_package_versions(self, link, search):
        """Return an InstallationCandidate or None"""
        platform = get_platform()

        version = None
        if link.egg_fragment:
            egg_info = link.egg_fragment
            ext = link.ext
        else:
            egg_info, ext = link.splitext()
            if not ext:
                self._log_skipped_link(link, 'not a file')
                return
            if ext not in SUPPORTED_EXTENSIONS:
                self._log_skipped_link(
                    link, 'unsupported archive format: %s' % ext)
                return
            if "binary" not in search.formats and ext == wheel_ext:
                self._log_skipped_link(
                    link, 'No binaries permitted for %s' % search.supplied)
                return
            if "macosx10" in link.path and ext == '.zip':
                self._log_skipped_link(link, 'macosx10 one')
                return
            if ext == wheel_ext:
                try:
                    wheel = Wheel(link.filename)
                except InvalidWheelFilename:
                    self._log_skipped_link(link, 'invalid wheel filename')
                    return
                if (pkg_resources.safe_name(wheel.name).lower() !=
                        search.canonical):
                    self._log_skipped_link(
                        link, 'wrong project name (not %s)' % search.supplied)
                    return
                if not wheel.supported():
                    self._log_skipped_link(
                        link, 'it is not compatible with this Python')
                    return
                # This is a dirty hack to prevent installing Binary Wheels from
                # PyPI unless it is a Windows or Mac Binary Wheel. This is
                # paired with a change to PyPI disabling uploads for the
                # same. Once we have a mechanism for enabling support for
                # binary wheels on linux that deals with the inherent problems
                # of binary distribution this can be removed.
                comes_from = getattr(link, "comes_from", None)
                if (
                        (
                            not platform.startswith('win') and not
                            platform.startswith('macosx') and not
                            platform == 'cli'
                        ) and
                        comes_from is not None and
                        urllib_parse.urlparse(
                            comes_from.url
                        ).netloc.endswith(PyPI.netloc)):
                    if not wheel.supported(tags=supported_tags_noarch):
                        self._log_skipped_link(
                            link,
                            "it is a pypi-hosted binary "
                            "Wheel on an unsupported platform",
                        )
                        return
                version = wheel.version

        # This should be up by the search.ok_binary check, but see issue 2700.
        if "source" not in search.formats and ext != wheel_ext:
            self._log_skipped_link(
                link, 'No sources permitted for %s' % search.supplied)
            return

        if not version:
            version = egg_info_matches(egg_info, search.supplied, link)
        if version is None:
            self._log_skipped_link(
                link, 'wrong project name (not %s)' % search.supplied)
            return

        if (link.internal is not None and not
                link.internal and not
                normalize_name(search.supplied).lower()
                in self.allow_external and not
                self.allow_all_external):
            # We have a link that we are sure is external, so we should skip
            #   it unless we are allowing externals
            self._log_skipped_link(link, 'it is externally hosted')
            self.need_warn_external = True
            return

        if (link.verifiable is not None and not
                link.verifiable and not
                (normalize_name(search.supplied).lower()
                    in self.allow_unverified)):
            # We have a link that we are sure we cannot verify its integrity,
            #   so we should skip it unless we are allowing unsafe installs
            #   for this requirement.
            self._log_skipped_link(
                link, 'it is an insecure and unverifiable file')
            self.need_warn_unverified = True
            return

        match = self._py_version_re.search(version)
        if match:
            version = version[:match.start()]
            py_version = match.group(1)
            if py_version != sys.version[:3]:
                self._log_skipped_link(
                    link, 'Python version is incorrect')
                return
        logger.debug('Found link %s, version: %s', link, version)

        return InstallationCandidate(search.supplied, version, link)
def _link_package_versions(self, link, search):
        """Return an InstallationCandidate or None"""
        platform = get_platform()

        version = None
        if link.egg_fragment:
            egg_info = link.egg_fragment
            ext = link.ext
        else:
            egg_info, ext = link.splitext()
            if not ext:
                self._log_skipped_link(link, 'not a file')
                return
            if ext not in SUPPORTED_EXTENSIONS:
                self._log_skipped_link(
                    link, 'unsupported archive format: %s' % ext)
                return
            if "binary" not in search.formats and ext == wheel_ext:
                self._log_skipped_link(
                    link, 'No binaries permitted for %s' % search.supplied)
                return
            if "macosx10" in link.path and ext == '.zip':
                self._log_skipped_link(link, 'macosx10 one')
                return
            if ext == wheel_ext:
                try:
                    wheel = Wheel(link.filename)
                except InvalidWheelFilename:
                    self._log_skipped_link(link, 'invalid wheel filename')
                    return
                if (pkg_resources.safe_name(wheel.name).lower() !=
                        search.canonical):
                    self._log_skipped_link(
                        link, 'wrong project name (not %s)' % search.supplied)
                    return
                if not wheel.supported():
                    self._log_skipped_link(
                        link, 'it is not compatible with this Python')
                    return
                # This is a dirty hack to prevent installing Binary Wheels from
                # PyPI unless it is a Windows or Mac Binary Wheel. This is
                # paired with a change to PyPI disabling uploads for the
                # same. Once we have a mechanism for enabling support for
                # binary wheels on linux that deals with the inherent problems
                # of binary distribution this can be removed.
                comes_from = getattr(link, "comes_from", None)
                if (
                        (
                            not platform.startswith('win') and not
                            platform.startswith('macosx') and not
                            platform == 'cli'
                        ) and
                        comes_from is not None and
                        urllib_parse.urlparse(
                            comes_from.url
                        ).netloc.endswith(PyPI.netloc)):
                    if not wheel.supported(tags=supported_tags_noarch):
                        self._log_skipped_link(
                            link,
                            "it is a pypi-hosted binary "
                            "Wheel on an unsupported platform",
                        )
                        return
                version = wheel.version

        # This should be up by the search.ok_binary check, but see issue 2700.
        if "source" not in search.formats and ext != wheel_ext:
            self._log_skipped_link(
                link, 'No sources permitted for %s' % search.supplied)
            return

        if not version:
            version = egg_info_matches(egg_info, search.supplied, link)
        if version is None:
            self._log_skipped_link(
                link, 'wrong project name (not %s)' % search.supplied)
            return

        if (link.internal is not None and not
                link.internal and not
                normalize_name(search.supplied).lower()
                in self.allow_external and not
                self.allow_all_external):
            # We have a link that we are sure is external, so we should skip
            #   it unless we are allowing externals
            self._log_skipped_link(link, 'it is externally hosted')
            self.need_warn_external = True
            return

        if (link.verifiable is not None and not
                link.verifiable and not
                (normalize_name(search.supplied).lower()
                    in self.allow_unverified)):
            # We have a link that we are sure we cannot verify its integrity,
            #   so we should skip it unless we are allowing unsafe installs
            #   for this requirement.
            self._log_skipped_link(
                link, 'it is an insecure and unverifiable file')
            self.need_warn_unverified = True
            return

        match = self._py_version_re.search(version)
        if match:
            version = version[:match.start()]
            py_version = match.group(1)
            if py_version != sys.version[:3]:
                self._log_skipped_link(
                    link, 'Python version is incorrect')
                return
        logger.debug('Found link %s, version: %s', link, version)

        return InstallationCandidate(search.supplied, version, link)
Return an InstallationCandidate or None