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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 all_selectors(Class, fn):

 """return a sorted list of selectors that occur in the stylesheet"""

        selectors = []
        cssparser = cssutils.CSSParser(validate=False)
        css = cssparser.parseFile(fn)
        for rule in [r for r in css.cssRules if type(r)==cssutils.css.CSSStyleRule]:
            selectors += [sel.selectorText for sel in rule.selectorList]
        selectors = sorted(list(set(selectors)))
        return selectors