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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 validate(self,value):
        '''
        Check for empty values, and for an existing template, but do not check if
        this is one of the initial choices provided.
        '''
        super(ChoiceField,self).validate(value)

        try:
            get_template(value)
        except TemplateDoesNotExist:
            raise ValidationError(_('%s is not a valid template.' % value))