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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 find_files(self):
        '''Find files in `paths` which match valid extensions'''
        for path in self.paths:
            for subpath, dirs, files in os.walk(path):
                for filename in files:
                    (name, ext) = os.path.splitext(filename)
                    if ext in self.extensions:
                        yield os.path.join(subpath, filename)