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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 build_regex(self, tokens):
 """Build compound regex from list of tokens"""

        patterns = []
        for token in tokens:
            patterns.append(token.pattern_start)
            if token.pattern_end:
                patterns.append(token.pattern_end)
        return re.compile('|'.join(patterns), re.DOTALL)