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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 isostr_to_datetime(dt_str):
 """ Converts iso formated text string into a datetime object Args: dt_str (str):
 ISO formated text string Returns: :obj:`datetime.datetime` """

    if len(dt_str) <= 20:
        return datetime.datetime.strptime(dt_str, "%Y-%m-%dT%H:%M:%SZ")
    else:
        dt_str = dt_str.split(".")
        return isostr_to_datetime("%sZ" % dt_str[0])