def remove(self, elem):
        """Remove a requirement.

        :param elem: a string or :class:`Requirement` instance.
        """
        if isinstance(elem, text_type):
            for requirement in self:
                if requirement.package == elem:
                    return super(Requirements, self).remove(requirement)
        return super(Requirements, self).remove(elem)
def test_bad_urls():
    values = [
        'foo',
        'http://',
        'http://example',
        'http://example.',
        'http://.com',
        'http://invalid-.com',
        'http://-invalid.com',
        'http://inv-.alid-.com',
        'http://inv-.-alid.com',
        'foo bar baz',
        u'foo \u2713',
        'http://@foo:bar@example.com',
        'http://:bar@example.com',
        'http://bar:bar:bar@example.com',
    ]

    for value in values:
        yield check_bad_url_raises, value