61   def commit_exists(self, commit):  argument
70     if not commit.rstrip():
73     _, _, err_code = self.git(['cat-file', '-e', commit])
76   def commit_date(self, commit):  argument
85     out, _, _ = self.git(['show', '-s', '--format=%ct', commit],
116   def get_parent(self, commit, count):  argument
123     out, _, err_code = self.git(['rev-parse', commit + '~' + str(count)],
167     commits = [commit for commit in commits if commit]
200   def checkout_commit(self, commit, clean=True):  argument
211     if not self.commit_exists(commit):
212       raise ValueError('Commit %s does not exist in current branch' % commit)
213     self.git(['checkout', '-f', commit], check_result=True)
216     if self.get_current_commit() != commit:
217       raise RuntimeError('Error checking out commit %s' % commit)