Python Looping Patterns and Event Handling
Explore Python coding patterns such as the Wait-Until-Event and Definite Loop patterns, illustrated with examples and images. Learn how to control loops based on specific events and conditions.
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Presentation Transcript
The Wait-Until-Event pattern Has it happened Has it happened Has it happened Has it happened Yes, it happened!
The Definite Loop pattern for k in range(...): ... ... window = zg.GraphWin('Animation', 650, 430) x = 20 y = 50 radius = 5 for k in range(150): circle = zg.Circle(zg.Point(x, y), radius) circle.setFill('purple') circle.draw(window) Determines how many times the loop iterates The body of the loop x = x + 2 y = y + 1 radius = radius + k / 100 time.sleep(0.01)
The Definite Loop pattern for k in range(...): ... ... window = zg.GraphWin('Animation', 650, 430) x = 20 y = 50 radius = 5 for k in range(150): circle = zg.Circle(zg.Point(x, y), radius) circle.setFill('purple') circle.draw(window) x = x + 2 y = y + 1 radius = radius + k / 100 time.sleep(0.01)
The Definite Loop pattern The Wait-Until-Event pattern Repeatedly: ... Has the event occurred? If so, break out of the loop. ... Run n times: ... ...
The Wait-Until-Event pattern Repeatedly: ... Has the event of interest occurred? If so, break out of the loop. ... Robot: Start moving. Repeatedly: Robot: Have you bumped into anything? If so, break out of the loop. Repeatedly: x = something input from the user if x is the sentinel value: break out of the loop Processx. Robot: Stop. 463 814 22 -1
The Wait-Until-Event pattern Expressed in Python using while True and break while True: ... if the event of interest occurred: break ... robot.go(..., 0) while True: sensor = 'BUMPS_AND_WHEEL_DROPS' bump = robot.getSensor(sensor) if bump[3] == 1 or bump[4] == 1: break while True: msg = 'Enter int, or -1 to stop' x = int(input(msg)) if x == -1: break Processx. robot.stop()
The Definite Loop pattern for k in range(...): ... ... Do the following 150 times: Draw a circle. Move and grow the circle. while True: ... if the event of interest occurred: break ... The Wait-Until-Event pattern Repeatedly draw, move and grow a circle, stopping when the circle grows beyond the border of the window. Do blah until the user asks you to stop. Robot, go until you hit a wall. Robot, go until your sensors say that you have gone 10 centimeters.
The Wait-Until-Event pattern while True: ... if the event of interest occurred: break ... Repeatedly draw, move and grow a circle, stopping when the circle grows beyond the border of the window. Do blah until the user asks you to stop. Robot, go until you hit a wall. Robot, go until your sensors say that you have gone 10 centimeters.
