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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 current(directory=None, verbose=False, head_only=False):
 """Display the current revision for each database."""

    config = current_app.extensions['migrate'].migrate.get_config(directory)
    if alembic_version >= (0, 7, 0):
        command.current(config, verbose=verbose, head_only=head_only)
    else:
        command.current(config)