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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 read_committed_file(gitref, filename):
 """Retrieve the content of a file in an old commit and returns it. Ketword Arguments: :gitref: (str) -- full reference of the git commit :filename: (str) -- name (full path) of the file Returns: str -- content of the file """

    repo = Repo()
    commitobj = repo.commit(gitref)

    blob = commitobj.tree[_delta_dir() + filename]
    return blob.data_stream.read()