How to force setuptools to use dependency link

from urllib import request
import re

def version_str_to_tuple(version_str):
    return tuple(map(int, version_str.split(".")))

def version_tuple_to_str(version_tuple):
    return ".".join(map(str, version_tuple))

_highest_version_cache = {}

def find_highest_version(package_name, repo_url="https://pypi.python.org/simple/"):
    if not package_name in _highest_version_cache:
        url = "%s%s/" % (repo_url, package_name)
        lines = request.urlopen(url).read().decode("utf-8").lower().splitlines()
        versions = []
        rgx = "%s-([0-9.]+)[.]tar[.]gz"%package_name
        compiled = re.compile(rgx)
        for line in lines:
            search_result = compiled.search(line)
            if search_result:
                versions += search_result.groups()
        _highest_version_cache[package_name] = max(
            map(
                version_str_to_tuple, versions
            )
        )
    return _highest_version_cache[package_name]

def inc(version_tuple):
    return version_tuple[:-1] + (version_tuple[-1] + 1, )

def vcs_requirement(package_name):
    return "%s<=%s" % (package_name,
                       version_tuple_to_str(
                           inc(
                               find_highest_version(
                                   package_name
                               )
                           )
                       )
    )

def egg_name(package_name):
    return "%s-%s" % (package_name,
                       version_tuple_to_str(
                           inc(
                               find_highest_version(
                                   package_name
                               )
                           )
                       )
    )

print(vcs_requirement("watchdog"))