For Loops¶

Assume a variable groceries has been defined to be a list of grocery items.

Write code to print out each item on its own line.
# replace this comment with your code ====

The for loop pattern is:

for item in list:

loop-body

for item in groceries: print(item)

Assume a variable groceries has been defined to be a list of grocery items.

Write code to print out all items in the list on separate lines, prefixed by the number of the item in the list. E.g.,
1. milk
2. eggs
3. chips
# replace this comment with your code ====
You will have to use an index-based loop, with range(len(groceries)) and indexing groceries as groceries[idx].

for idx in range(len(groceries)): print(str(idx + 1) + '. ' + groceries[idx])

Assume a variable groceries has been defined to be a list of grocery items.

Write code to print out all items in the list on a single line, separated by commas. It is OK to have a comma after the last item.
# replace this comment with your code ====

Remember that you can use print(..., end='') to keep the cursor on the same line.

for item in groceries: print(item, end=', ')

Write a for loop to sum up all numbers from 0 to n - 1 into a variable sum. Assume n is already defined. # replace this comment with your code ==== from unittest.gui import TestCaseGui class myTests(TestCaseGui): def testOne(self): self.assertEqual(sum, 45) myTests().main()
Your code should have this format:
- initialize sum to 0.
- for loop, using range.
  
  add the value to sum
sum = 0 for num in range(0, n): sum = sum + num

Write a for loop to print out each letter in a str name on one line with a space between. # replace this comment with your code ====

A string is iterable, so you can use it right in the for loop:

e.g.,

for char in str:

for char in name: print(char, end=' ')

Write a for loop to iterate over a string name and print every other letter – i.e., the letters with indices which are even. That is, only the 0th, 2nd, 4th, etc., letters. # replace this comment with your code ====

Use an index-based loop, since you will need to know if you are looking at an even or odd index.

Use an if statement in the for loop to determine if the index is even.

for idx in range(len(name)): if idx % 2 == 0: print(name[idx])

Write code to create a list rands that contains 20 random numbers from 0 to 100 inclusive. from random import randint # replace this comment with your code ==== from unittest.gui import TestCaseGui class myTests(TestCaseGui): def testOne(self): self.assertEqual(len(rands), 20) for item in rands: self.assertTrue(item >= 0 and item <= 100) myTests().main()

Above the for loop, create the variable rands to be an empty list.

Call randint(0, 100) to get random integers from 0 to 100, inclusive.

Use append() to add a random number to the list.

Use range(20) to iterate 20 times.

from random import randint rands = [] for idx in range(20): rands.append(randint(0, 100))

Write a for loop to create a list tenths containing numbers 0.0, 0.1, 0.2, 0.3, 0.4, …, 9.9 # replace this comment with your code ==== from unittest.gui import TestCaseGui class myTests(TestCaseGui): def testOne(self): self.assertEqual(len(tenths), 100) self.assertAlmostEqual(tenths[0], 0.0) self.assertAlmostEqual(tenths[99], 9.9) self.assertAlmostEqual(tenths[50], 5.0) myTests().main()

Above the for loop, create the variable tenths to be an empty list.

There will be 100 numbers in the list, so use range(100) to iterate 100 times.

tenths = [] for i in range(100): tenths.append(i / 10)

Given a list numbers, write code to print Found it! if the list contains the number 7. Do not use the in operator. Use a for loop, with an if statement in it. # replace this comment with your code ====

Use item-based iteration. Put a simple if statement in the for loop.

for num in numbers: if num == 7: print("Found it!")

Given a list numbers, write code to create two lists, bignums and littlenums, by adding each number in numbers to bignums if it is greater than 50, and adding all the other numbers to littlenums. # replace this comment with your code ==== from unittest.gui import TestCaseGui class myTests(TestCaseGui): def testOne(self): self.assertEqual(len(littlenums) + len(bignums), len(numbers)) self.assertTrue(50 in littlenums, "50 should be in littlenums") self.assertEqual(len(littlenums), 8) self.assertTrue(99.22 in bignums) myTests().main()

Create the resulting lists before the for loop.

Use item-based iteration with an if-else in it.

bignums = [] littlenums = [] for num in numbers: if num > 50: bignums.append(num) else: littlenums.append(num)

This code was recently seen in a project:

block_list = [Block(20,20), Block(20,60), Block(20,100), Block(20,140), Block(20,180), Block(60,20), Block(60,60), Block(60,100), Block(60,140), Block(60,180), Block(100,20), Block(100,60), Block(100,100), Block(100,140), Block(100,180), Block(140,20), Block(140,60), Block(140,100), Block(140,140), Block(140,180), Block(180,20), Block(180,60), Block(180,100), Block(180,140), Block(180,180), Block(220,20), Block(220,60), Block(220,100), Block(220,140), Block(220,180),Block(260,20), Block(260,60), Block(260,100), Block(260,140), Block(260,180), Block(300,20), Block(300,60), Block(300,100), Block(300,140), Block(300,180), Block(340,20), Block(340,60), Block(340,100), Block(340,140), Block(340,180), Block(380,20), Block(380,60), Block(380,100), Block(380,140), Block(380,180), Block(420,20), Block(420,60), Block(420,100), Block(420,140), Block(420,180), Block(460,20), Block(460,60), Block(460,100), Block(460,140), Block(460,180), Block(500,20), Block(500,60), Block(500,100), Block(500,140), Block(500,180), Block(540,20), Block(540,60), Block(540,100), Block(540,140), Block(540,180), Block(580,20), Block(580,60), Block(580,100), Block(580,140), Block(580,180), Block(620,20), Block(620,60), Block(620,100), Block(620,140), Block(620,180), Block(660,20), Block(660,60), Block(660,100), Block(660,140), Block(660,180), Block(700,20), Block(700,60), Block(700,100), Block(700,140), Block(700,180)]

Rewrite this code to use a doubly-nest for loop.
block_list = [] # add your code below ==== from unittest.gui import TestCaseGui class myTests(TestCaseGui): def testOne(self): self.assertEqual(len(block_list), 90) myTests().main()

Create the resulting list before the for loops.

Create a for loop to iterate from 20 to 700, by 40s.

Inside the first for loop, write a for loop to iterate from 20 to 180 by 40s.

Inside that for loop, call the Block() call, and append the result to your block_list.

block_list = [] for vert in range(20, 701, 40): for horiz in range(20, 181, 40): block_list.append(Block(vert, horiz))

Integers are used as indices into sequences, like lists and strings. So, if you want to access each element in a sequence at a certain index, you need to use a for loop to iterate over each index appropriate for accessing the sequence at that index.

To get the indices appropriate for indexing a sequence, use range(len(sequence)).

Replace <1> in the following code with a call to range(len(sequence)) so that the for loop prints out all indices useful for indexing into the sequence groceries.
for idx in <1>: print(idx) ====

len(groceries) returns the number of items in the sequence.

for idx in range(len(groceries)): # print out the index for this item in the groceries list. print(idx)

Replace <1> in the following code with a call to range(len(sequence)) so that the for loop uses indexes useful for indexing into the sequence groceries.

Replace <2> with code to access the value in sequence groceries at index idx.

Your resulting code should print each item in the groceries list, regardless of how long the groceries list is.
for idx in <1>: print(<2>) ====

len(groceries) returns the number of items in the sequence.

for idx in range(len(groceries)): print(groceries[idx])

Replace <1> in the code so that the for loop prints each item except the last in the list groceries. for idx in <1>: print(groceries[idx]) ====

len(groceries) returns the number of items in the sequence, but we want to access all items except the last one, so subtract one from that value.

for idx in range(len(groceries) - 1): print(groceries[idx])

Replace <1> in the code so that the for loop prints each item except the first and the last in the list groceries. for idx in <1>: print(groceries[idx]) ====

To skip the first item, start with index 1, not the default of 0.

len(groceries) returns the number of items in the sequence, but we want to access all items except the last one, so subtract one from that value.

for idx in range(1, len(groceries) - 1): print(groceries[idx])

Replace <1> in the code so that the for loop prints each item in the list groceries in reverse order. Use range() with a step of -1. for idx in <1>: print(groceries[idx]) ====

You need to use all three parameters to range. The start value needs to be the index of the last element of groceries – so get the length of groceries and subtract 1. The stop value needs to be less than 0, so that 0 is the last index that range generates.

for idx in range(len(groceries) - 1, -1, -1): print(groceries[idx])