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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 pattern(self):
 """ Regular expression describing valid objects. .. note:: JSON schema specifications says that this value SHOULD follow the ``EMCA 262/Perl 5`` format. We cannot support this so we support python regular expressions instead. This is still valid but should be noted for clarity. :returns: None or compiled regular expression """

        value = self._schema.get("pattern", None)
        if value is None:
            return
        try:
            return re.compile(value)
        except re.error as ex:
            raise SchemaError(
                "pattern value {0!r} is not a valid regular expression:"
                " {1}".format(value, str(ex)))