add sleep time to show
In every effect there are at least one time the lines: ```python lp.show() time.sleep(t) ``` To write one less line every time after show, these lines could be: ```python lp.show(t) ``` If lp.show() had a parameter for sleeptime and call time.sleep(t) if t > 0. `t` has to be optional with default value `0`.
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