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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 is_docstring(tokens, previous_logical):
 """Return found docstring 'A docstring is a string literal that occurs as the first statement in a module, function, class,' http://www.python.org/dev/peps/pep-0257/#what-is-a-docstring """

    for token_type, text, start, _, _ in tokens:
        if token_type == tokenize.STRING:
            break
        elif token_type != tokenize.INDENT:
            return False
    else:
        return False
    line = text.lstrip()
    start, start_triple = _find_first_of(line, START_DOCSTRING_TRIPLE)
    if (previous_logical.startswith("def ") or
            previous_logical.startswith("class ")):
        if start == 0:
            return text