docs: def find_assign(data, varname):
      """Finds a substring that looks like an assignment.
  
      :param data: Source to search in.
      :param varname: Name of the variable for which an assignment should be
                      found.
      """
      ASSIGN_RE = re.compile(BASE_ASSIGN_PATTERN.format(varname))
  
      if len(ASSIGN_RE.findall(data)) > 1:
          raise PluginError('Found multiple {}-strings.'.format(varname))
  
      if len(ASSIGN_RE.findall(data)) < 1:
          raise PluginError('No version assignment ("{}") found.'
                            .format(varname))
  
      return ASSIGN_RE.search(data).group(2)