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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 split_header(line):
 """ Split a header line into field name and field value. Note that custom fields may contain colons inside the curly braces, so we need a special test for them. :param line: A message line to be split. :returns: (Field name, field value) tuple. """

        match = re.match(r'^(CF\.\{.*?}): (.*)$', line)
        if match:
            return (match.group(1), match.group(2))
        return line.split(': ', 1)