code: def identify_vcs(repo_url, guess=False, repo_aliases=REPO_ALIASES):
      
      repo_url = unicode(repo_url)
  
      # Do basic alias check
      vcs = identify_vcs_vs_alias(repo_url, guess=guess, repo_aliases=repo_aliases)
      if vcs:
          return vcs
  
      # remove prefix and try again
      no_prefix = ''.join(repo_url.split("//")[1:])
      vcs = identify_vcs_vs_alias(no_prefix, guess=guess, repo_aliases=repo_aliases)
      if vcs:
          return vcs
  
      if guess:
          if "bitbucket" in repo_url:
              return "hg"
  
      raise UnknownVCS
docs: Determines the type of repo that `repo_url` represents.
      :param repo_url: Repo URL of unknown type.
      :returns: VCS type (git, hg, etc) or raises UnknownVCS exception.