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COMP 1000: Think Like a Computer The PreTeXt Interactive Edition

Section 4.6 Strings and for loops

Since a string is simply a sequence of characters, the for loop iterates over each character automatically. (As always, try to predict what the output will be from this code before you run it.)
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The loop variable achar is automatically assigned each character in the string “Go Spot Go” one at a time. We will refer to this type of sequence iteration as iteration by item. Note that the for loop processes the characters in a string or items in a sequence one at a time from left to right.
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Check your understanding
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Checkpoint 4.6.1.

How many times is the word HELLO printed by the following statements?
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s = "python rocks"
for ch in s:
   print("HELLO")
  • 10
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  • Iteration by item will process once for each item in the sequence.
  • 11
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  • The blank is part of the sequence.
  • 12
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  • Yes, there are 12 characters, including the blank.
  • Error, the for statement needs to use the range function.
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  • The for statement can iterate over a sequence item by item.
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Checkpoint 4.6.2.

How many times does the turtle in this code move to a random location?
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# Turtle name symbol drawing
import turtle
import random
wn = turtle.Screen()
annika = turtle.Turtle()
s = input("Please enter your name")
for ch in s:
   x = random.randrange(-200, 200)
   y = random.randrange(-150, 150)
   annika.goto(x, y)
  • The turtle will move to as many locations as there are letters in the name.
  • The turtle will move to at least one location.
  • The turtle will move to as many locations as there are letters in the name.
  • It depends on the length of the name the user enters.
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  • Yes, if the user enters "Sam", the turtle will move to 3 random locations.
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