for loops with range (class slides)

CSc 110 - for loops with range

while vs. for loops

In addition to while, we can use for to create loops

values = [70, 20, 30]
index = 0
while index < len(values):
  print(values[index])
  index += 1

70
20
30

values = [70, 20, 30]
for index in range(len(values)):
  print(values[index])

70
20
30

Write a function

1. Its name is make_all_even
2. It takes one argument, a list of integers
3. It iterates over the list, changing odd numbers to even number (even up)
4. Use a for loop

test_integers = [1, 2, 3, 4]
assert make_all_even(test_integers) == [2, 2, 4, 4]

Write a function – solution

def make_all_even(integers):
  # for each index in list
  for index in range(len(integers)):
    integers[index] += integers[index] % 2 # add zero if even, one if odd
  return integers
      
def main():
  test_integers = [1, 2, 3, 4]
  assert make_all_even(test_integers) == [2, 2, 4, 4]
  print(test_integers) # we print the list we created before function call
  
main()

[2, 2, 4, 4]

Write a function

1. Its name is indices_of_vowels
2. It takes a single string as its parameter.
3. It returns a list of integers that represent the indices of the vowels in the original list
4. Use a for loop

Test cases:

assert indices_of_vowels("hello") == [1, 4]
assert indices_of_vowels("") == []
assert indices_of_vowels("aeiou") == [0, 1, 2, 3, 4]

Write a function – solution

def indices_of_vowels(string):
  result = [] # initialize empty list to hold indices
  # for every index in list
  for index in range(len(string)):
    if string[index] in "aeiou": # check if character is vowel
      result.append(index) # append index to result
  return result

def main():
  assert indices_of_vowels("hello") == [1, 4]
  assert indices_of_vowels("") == []
  assert indices_of_vowels("aeiou") == [0, 1, 2, 3, 4]

main()

Submit code for attendance

Submit your indices_of_vowels functions to Gradescope for attendance.

Name your file indices_of_vowels.py

More on how to use range()

Syntax: range(start, stop, step)

• start Optional. An integer number specifying at which position to start. Default is 0
• stop Required. An integer number specifying at which position to stop (not included).
• step Optional. An integer number specifying the incrementation. Default is 1

More on how to use range()

for n in range(5):
  print(n)

0
1
2
3
4

for n in range(0, 5, 1):
  print(n)

0
1
2
3
4

for n in range(0, 5, 2):
  print(n)

0
2
4

Write a function

1. Its name is every_two_together
2. It takes one argument, a list of characters
3. It creates a new string with items at even indices in characters concatenated together
4. It returns the string created
5. Use a for loop

Test cases:

characters = ["a", "e", "p", "o", "p", "w", "l", "i", "e", "f"]
assert every_two_together(characters) == "apple"

Write a function – solution

What other test cases should we run?

def every_two_together(chars):
  new_string = ""
  for i in range(0, len(chars), 2):
    new_string += chars[i]
  return new_string

def main():
  characters = ["a", "e", "p", "o", "p", "w", "l", "i", "e", "f"]
  assert every_two_together(characters) == "apple"
  
main()

Write a function

Test cases:

my_numbers = [0, 1, 0, 3, 0]
assert add_every_two(my_numbers) == 0

Write a function – solution

def add_every_two(numbers):
  result = 0
  for i in range(0, len(numbers), 2):
    result += numbers[i]
  return result

def main():
  my_numbers = [0, 1, 0, 3, 0]
  assert add_every_two(my_numbers) == 0
  
main()