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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 edit(directory=None, revision='current'):
 """Edit current revision."""

    if alembic_version >= (0, 8, 0):
        config = current_app.extensions['migrate'].migrate.get_config(
            directory)
        command.edit(config, revision)
    else:
        raise RuntimeError('Alembic 0.8.0 or greater is required')