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328 lines
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[#]: subject: "How I rediscovered Logo with the Python Turtle module"
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[#]: via: "https://opensource.com/article/21/9/logo-python-turtle"
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[#]: author: "Ayush Sharma https://opensource.com/users/ayushsharma"
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[#]: collector: "lujun9972"
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[#]: translator: " "
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[#]: reviewer: " "
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[#]: publisher: " "
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[#]: url: " "
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How I rediscovered Logo with the Python Turtle module
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======
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The Logo programming language is available today as a Python package.
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![Box turtle][1]
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When I was in high school, one of the very first programming languages I was introduced to was Logo. It was interactive and visual. With basic movement commands, you could have your cursor (“turtle”) draw basic shapes and intricate patterns. It was a great way to introduce the compelling concept of an algorithm—a series of instructions for a computer to execute.
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Fortunately, the Logo programming language is available today as a Python package. So let’s jump right in, and you can discover the possibilities with Logo as we go along.
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### Installing the Turtle module
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Logo is available as the [`turtle` package for Python][2]. To use it, you must have Python installed first. Python is already installed on Linux and BSD, and it's easy to install on both [MacOS][3] and [Windows][4].
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Once you have Python installed, install the Turtle module:
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```
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`pip3 install turtle`
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```
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### Bob draws a square
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With the `turtle` package installed, you can draw some basic shapes.
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To draw a square, imagine a turtle (call him Bob) in the middle of your screen, holding a pen with his tail. Every time Bob moves, he draws a line behind him. How must Bob move to draw a square?
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1. Move forward 100 steps.
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2. Turn right 90 degrees.
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3. Move forward 100 steps.
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4. Turn right 90 degrees.
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5. Move forward 100 steps.
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6. Turn right 90 degrees.
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7. Move forward 100 steps.
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Now write the above algorithm in Python. Create a file called `logo.py` and place the following code in it.
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```
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import turtle
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if __name__ == '__main__':
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turtle.title('Hi! I\'m Bob the turtle!')
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turtle.setup(width=800, height=800)
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bob = turtle.Turtle(shape='turtle')
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bob.color('orange')
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# Drawing a square
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bob.forward(100)
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bob.right(90)
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bob.forward(100)
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bob.right(90)
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bob.forward(100)
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bob.right(90)
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bob.forward(100)
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turtle.exitonclick()
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```
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Save the above as `logo.py` and run it:
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```
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`$ python3 logo.py`
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```
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Bob draws a square on the screen:
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![Logo drawn square][5]
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Illustration by Ayush Sharma, [CC BY-SA 4.0][6]
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### Bob draws a hexagon
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To draw a hexagon, Bob must move like this:
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1. Move forward 150 steps.
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2. Turn right 60 degrees.
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3. Move forward 150 steps.
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4. Turn right 60 degrees.
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5. Move forward 150 steps.
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6. Turn right 60 degrees.
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7. Move forward 150 steps.
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8. Turn right 60 degrees.
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9. Move forward 150 steps.
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10. Turn right 60 degrees.
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11. Move forward 150 steps.
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In Python, you can use a [`for` loop][7] to move Bob:
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```
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import turtle
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if __name__ == '__main__':
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turtle.title('Hi! I\'m Bob the turtle!')
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turtle.setup(width=800, height=800)
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bob = turtle.Turtle(shape='turtle')
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bob.color('orange')
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# Drawing a hexagon
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for i in range(6):
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bob.forward(150)
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bob.right(60)
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turtle.exitonclick()
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```
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Run your code again and watch Bob draw a hexagon.
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![Logo drawn hexagon][8]
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Illustration by Ayush Sharma, [CC BY-SA 4.0][6]
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### Bob draws a square spiral
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Now try drawing a square spiral, but this time you can speed things up a bit. You can use the `speed` function and set `bob.speed(2000)` so that Bob moves faster.
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```
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import turtle
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if __name__ == '__main__':
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turtle.title('Hi! I\'m Bob the turtle!')
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turtle.setup(width=800, height=800)
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bob = turtle.Turtle(shape='turtle')
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bob.color('orange')
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# Drawing a square spiral
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bob.speed(2000)
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for i in range(500):
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bob.forward(i)
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bob.left(91)
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turtle.exitonclick()
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```
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![Logo drawn spiral][9]
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Illustration by Ayush Sharma, [CC BY-SA 4.0][6]
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### Bob and Larry draw a weird snake thing
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In the above examples, you initialized `Bob` as an object of the `Turtle` class. You're not limited to just one turtle, though. In the next code block, create a second turtle called `Larry` to draw along with Bob.
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The `penup()` function makes the turtles lift their pens, so they don’t draw anything as they move, and the `stamp()` function places a marker whenever it’s called.
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```
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import turtle
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if __name__ == '__main__':
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turtle.title('Hi! We\'re Bob and Larry!')
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turtle.setup(width=800, height=800)
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bob = turtle.Turtle(shape='turtle')
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larry = turtle.Turtle(shape='turtle')
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bob.color('orange')
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larry.color('purple')
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bob.penup()
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larry.penup()
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bob.goto(-180, 200)
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larry.goto(-150, 200)
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for i in range(30, -30, -1):
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bob.stamp()
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larry.stamp()
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bob.right(i)
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larry.right(i)
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bob.forward(20)
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larry.forward(20)
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turtle.exitonclick()
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```
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![Logo drawn snake][10]
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Illustration by Ayush Sharma, [CC BY-SA 4.0][6]
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### Bob draws a sunburst
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Bob can also draw simple lines and fill them in with color. The functions `begin_fill()` and `end_fill()` allow Bob to fill a shape with the color set with `fillcolor()`.
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```
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import turtle
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if __name__ == '__main__':
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turtle.title('Hi! I\'m Bob the turtle!')
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turtle.setup(width=800, height=800)
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bob = turtle.Turtle(shape='turtle')
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bob.color('orange')
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# Drawing a filled star thingy
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bob.speed(2000)
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bob.fillcolor('yellow')
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bob.pencolor('red')
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for i in range(200):
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bob.begin_fill()
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bob.forward(300 - i)
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bob.left(170)
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bob.forward(300 - i)
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bob.end_fill()
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turtle.exitonclick()
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```
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![Logo drawn sunburst][11]
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Illustration by Ayush Sharma, [CC BY-SA 4.0][6]
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### Larry draws a Sierpinski triangle
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Bob enjoys drawing simple geometrical shapes holding a pen with his tail as much as the next turtle, but what he enjoys most is drawing fractals.
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One such shape is the [Sierpinski triangle][12], which is an equilateral triangle recursively subdivided into smaller equilateral triangles. It looks something like this:
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![Logo drawn triangle][13]
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Illustration by Ayush Sharma, [CC BY-SA 4.0][6]
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To draw the Sierpinski triangle above, Bob has to work a bit harder:
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```
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import turtle
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def get_mid_point(point_1: list, point_2: list):
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return ((point_1[0] + point_2[0]) / 2, (point_1[1] + point_2[1]) / 2)
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def triangle(turtle: turtle, points, depth):
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turtle.penup()
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turtle.goto(points[0][0], points[0][1])
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turtle.pendown()
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turtle.goto(points[1][0], points[1][1])
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turtle.goto(points[2][0], points[2][1])
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turtle.goto(points[0][0], points[0][1])
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if depth > 0:
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triangle(turtle, [points[0], get_mid_point(points[0], points[1]), get_mid_point(points[0], points[2])], depth-1)
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triangle(turtle, [points[1], get_mid_point(points[0], points[1]), get_mid_point(points[1], points[2])], depth-1)
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triangle(turtle, [points[2], get_mid_point(points[2], points[1]), get_mid_point(points[0], points[2])], depth-1)
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if __name__ == '__main__':
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turtle.title('Hi! I\'m Bob the turtle!')
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turtle.setup(width=800, height=800)
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larry = turtle.Turtle(shape='turtle')
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larry.color('purple')
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points = [[-175, -125], [0, 175], [175, -125]] # size of triangle
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triangle(larry, points, 5)
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turtle.exitonclick()
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```
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### Wrap up
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The Logo programming language is a great way to teach basic programming concepts, such as how a computer can execute a set of commands. Also, because the library is now available in Python, it can be used to visualize complex ideas and concepts.
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I hope Bob and Larry have been enjoyable and instructive.
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Have fun, and happy coding.
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* * *
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_This article was originally published on the [author's personal blog][14] and has been adapted with permission._
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/21/9/logo-python-turtle
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作者：[Ayush Sharma][a]
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选题：[lujun9972][b]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://opensource.com/users/ayushsharma
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[b]: https://github.com/lujun9972
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[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/patti-black-unsplash.jpg?itok=hS8wQNUg (Box turtle)
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[2]: https://docs.python.org/3.7/library/turtle.html
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[3]: https://opensource.com/article/19/5/python-3-default-mac
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[4]: https://opensource.com/article/19/8/how-install-python-windows
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[5]: https://opensource.com/sites/default/files/uploads/rediscovering-logo-python-turtle-square.jpg (Logo drawn square)
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[6]: https://creativecommons.org/licenses/by-sa/4.0/
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[7]: https://opensource.com/article/18/3/loop-better-deeper-look-iteration-python
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[8]: https://opensource.com/sites/default/files/uploads/rediscovering-logo-python-turtle-hexagon.jpg (Logo drawn hexagon)
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[9]: https://opensource.com/sites/default/files/uploads/rediscovering-logo-python-turtle-square-spiral.jpg (Logo drawn spiral)
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[10]: https://opensource.com/sites/default/files/uploads/rediscovering-logo-python-turtle-stamping-larry.jpg (Logo drawn snake)
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[11]: https://opensource.com/sites/default/files/uploads/rediscovering-logo-python-turtle-sunburst.jpg (Logo drawn sunburst)
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[12]: https://en.wikipedia.org/wiki/Sierpinski_triangle
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[13]: https://opensource.com/sites/default/files/uploads/rediscovering-logo-python-turtle-sierpinski-triangle.jpg (Logo drawn triangle)
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[14]: https://notes.ayushsharma.in/2019/06/rediscovering-logo-with-bob-the-turtle
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