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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def egg_link_path(dist):
 # type: (Distribution) -> Optional[str] """ Return the path for the .egg-link file if it exists, otherwise, None. There's 3 scenarios: 1) not in a virtualenv try to find in site.USER_SITE, then site_packages 2) in a no-global virtualenv try to find in site_packages 3) in a yes-global virtualenv try to find in site_packages, then site.USER_SITE (don't look in global location) For #1 and #3, there could be odd cases, where there's an egg-link in 2 locations. This method will just return the first one found. """

    sites = []
    if running_under_virtualenv():
        if virtualenv_no_global():
            sites.append(site_packages)
        else:
            sites.append(site_packages)
            if user_site:
                sites.append(user_site)
    else:
        if user_site:
            sites.append(user_site)
        sites.append(site_packages)

    for site in sites:
        egglink = os.path.join(site, dist.project_name) + '.egg-link'
        if os.path.isfile(egglink):
            return egglink
    return None