code: def check_pypi_exists(dependencies):
      
      for dependency in dependencies.get('pypi', []):
          logger.debug("Checking if %r exists in PyPI", dependency)
          try:
              exists = _pypi_head_package(dependency)
          except Exception as error:
              logger.error("Error checking %s in PyPI: %r", dependency, error)
              raise FadesError("Could not check if dependency exists in PyPI")
          else:
              if not exists:
                  logger.error("%s doesn't exists in PyPI.", dependency)
                  return False
      return True
docs: Check if the indicated dependencies actually exists in pypi.