code: def find_revision_id(self, revision=None):
          
          # Make sure the local repository exists.
          self.create()
          # Try to find the revision id of the specified revision.
          revision = self.expand_branch_name(revision)
          output = self.context.capture('git', 'rev-parse', revision)
          # Validate the `git rev-parse' output.
          return self.ensure_hexadecimal_string(output, 'git rev-parse')
docs: Find the global revision id of the given revision.