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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 extract_vars(template):
 """ Extract variables from template. Variables are enclosed in double curly braces. """

    keys = set()
    for match in re.finditer(r"\{\{ (?P<key>\w+) \}\}", template.getvalue()):
        keys.add(match.groups()[0])
    return sorted(list(keys))