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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 read_manifest():
 """Read existing configuration from MANIFEST.in. We use that to ignore anything the MANIFEST.in ignores. """

    # XXX modifies global state, which is kind of evil
    if not os.path.isfile('MANIFEST.in'):
        return
    ignore, ignore_regexps = _get_ignore_from_manifest('MANIFEST.in')
    IGNORE.extend(ignore)
    IGNORE_REGEXPS.extend(ignore_regexps)