code: def _generate_git_header(packagename, version, githash):
      
  
      loader = pkgutil.get_loader(git_helpers)
      source = loader.get_source(git_helpers.__name__) or ''
      source_lines = source.splitlines()
      if not source_lines:
          log.warn('Cannot get source code for astropy_helpers.git_helpers; '
                   'git support disabled.')
          return ''
  
      idx = 0
      for idx, line in enumerate(source_lines):
          if line.startswith('# BEGIN'):
              break
      git_helpers_py = '\n'.join(source_lines[idx + 1:])
  
      verstr = version
  
      new_githash = git_helpers.get_git_devstr(sha=True, show_warning=False)
  
      if new_githash:
          githash = new_githash
  
      return _FROZEN_VERSION_PY_WITH_GIT_HEADER.format(
                  git_helpers=git_helpers_py, packagename=packagename,
                  verstr=verstr, githash=githash)
docs: Generates a header to the version.py module that includes utilities for
      probing the git repository for updates (to the current git hash, etc.)
      These utilities should only be available in development versions, and not
      in release builds.
  
      If this fails for any reason an empty string is returned.