req_install.py 文件源码

def from_req(cls, req, comes_from=None, isolated=False, wheel_cache=None):
        try:
            req = Requirement(req)
        except InvalidRequirement:
            raise InstallationError("Invalid requirement: '%s'" % req)
        if req.url:
            raise InstallationError(
                "Direct url requirement (like %s) are not allowed for "
                "dependencies" % req
            )
        return cls(req, comes_from, isolated=isolated, wheel_cache=wheel_cache)