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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 _get_template(querystring_key, mapping):
 """Return the template corresponding to the given ``querystring_key``."""

    default = None
    try:
        template_and_keys = mapping.items()
    except AttributeError:
        template_and_keys = mapping
    for template, key in template_and_keys:
        if key is None:
            key = PAGE_LABEL
            default = template
        if key == querystring_key:
            return template
    return default