Retrieve given file path contents of certain Git revision.

def from_git_rev_read(path):
    """Retrieve given file path contents of certain Git revision."""
    if ":" not in path:
        raise ValueError("Path identifier must start with a revision hash.")

    cmd = "git", "show", "-t", path
    try:
        return subprocess.check_output(cmd).rstrip().decode("utf-8")
    except subprocess.CalledProcessError:
        raise ValueError