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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 revert(context, file_names):
 """Revert each file in the list file_names back to version in repo"""

    context.obj.find_repo_type()
    if len(file_names) == 0:
        click.echo('No file names to checkout specified.')
        click.echo('The following have changed since the last check in.')
        context.invoke(status)
    for fn in file_names:
        if context.obj.vc_name == 'git':
            context.obj.call(['git', 'checkout', '--', fn])
        elif context.obj.vc_name == 'hg':
            context.obj.call(['hg', 'revert', '--no-backup', fn])