How to use 'python open' in Python

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def open_python_file(filename):
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    """Open a read-only Python file taking proper care of its encoding.
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    In Python 3, we would like all files to be opened with utf-8 encoding.
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    However, some author like to specify PEP263 headers in their source files
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    with their own encodings. In that case, we should respect the author's
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    encoding.
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    """
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    import tokenize
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    if hasattr(tokenize, "open"):  # Added in Python 3.2
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        # Open file respecting PEP263 encoding. If no encoding header is
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        # found, opens as utf-8.
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        return tokenize.open(filename)
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    else:
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        return open(filename, "r")