docs: def get_install_requires():
      """Add conditional dependencies (when creating source distributions)."""
      install_requires = get_requirements('requirements.txt')
      if 'bdist_wheel' not in sys.argv:
          if sys.version_info[0] == 2:
              # On Python 2.6 and 2.7 we pull in Bazaar.
              install_requires.append('bzr >= 2.6.0')
          if sys.version_info[2:] == (2, 6):
              # On Python 2.6 we have to stick to versions of Mercurial below 4.3
              # because 4.3 drops support for Python 2.6, see the change log:
              # https://www.mercurial-scm.org/wiki/WhatsNew
              install_requires.append('mercurial >= 2.9, < 4.3')
          elif (2, 6) < sys.version_info[:2] < (3, 0):
              # On Python 2.7 we pull in Mercurial.
              install_requires.append('mercurial >= 2.9')
      return sorted(install_requires)