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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 watch():
 """Renerate documentation when it changes."""


    # Start with a clean build
    sphinx_build['-b', 'html', '-E', 'docs', 'docs/_build/html'] & FG

    handler = ShellCommandTrick(
        shell_command='sphinx-build -b html docs docs/_build/html',
        patterns=['*.rst', '*.py'],
        ignore_patterns=['_build/*'],
        ignore_directories=['.tox'],
        drop_during_process=True)
    observer = Observer()
    observe_with(observer, handler, pathnames=['.'], recursive=True)