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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_commit_log(from_rev=None):
 """ Yields all commit messages from last to first. """


    check_repo()
    rev = None
    if from_rev:
        rev = '...{from_rev}'.format(from_rev=from_rev)
    for commit in repo.iter_commits(rev):
        yield (commit.hexsha, commit.message)