Iterating over lists in Python - Mini Project: Build & Apply

Iterating over lists

📖 Scenario: You are helping a small bookstore organize its daily sales data. The store records the number of books sold each day in a list. You will write a simple program to go through this list and work with the sales numbers.

🎯 Goal: Build a program that creates a list of daily book sales, sets a target sales number, counts how many days met or exceeded the target using a loop, and then prints the count.

📋 What You'll Learn

Create a list called daily_sales with the exact values: 12, 7, 15, 9, 20, 5

Create a variable called target and set it to 10

Use a for loop with the variable sales to iterate over daily_sales

Inside the loop, count how many days have sales greater than or equal to target

Print the final count using print(count)

💡 Why This Matters

🌍 Real World

Counting how many days meet a sales goal helps businesses understand their performance and plan better.

💼 Career

This skill is useful for data analysis, reporting, and automating simple business tasks.

1

Create the daily sales list

Create a list called daily_sales with these exact values: 12, 7, 15, 9, 20, 5

Python

# Create the list daily_sales with the values 12, 7, 15, 9, 20, 5
# Your code here

Hint

Use square brackets [] to create a list and separate numbers with commas.

2

Set the target sales number

Create a variable called target and set it to the number 10

Python

daily_sales = [12, 7, 15, 9, 20, 5]
# Create the variable target and set it to 10
# Your code here

Hint

Use the equals sign = to assign the value 10 to the variable target.

3

Count days meeting the target

Create a variable called count and set it to 0. Then use a for loop with the variable sales to iterate over daily_sales. Inside the loop, add 1 to count if sales is greater than or equal to target.

Python

daily_sales = [12, 7, 15, 9, 20, 5]
target = 10
# Create count = 0
# Use for sales in daily_sales:
#   If sales >= target, add 1 to count
# Your code here

Hint

Start with count = 0. Use a for loop to check each sales. Use an if statement to compare sales with target. Increase count by 1 when condition is true.

4

Print the count

Write a print statement to display the value of count

Python

daily_sales = [12, 7, 15, 9, 20, 5]
target = 10
count = 0
for sales in daily_sales:
    if sales >= target:
        count += 1
# Print the count
# Your code here

Hint

Use print(count) to show the final number of days meeting the target.

Practice

1. What does the following code do?

for item in [1, 2, 3]:
    print(item)

easy

A. Prints the whole list once

B. Prints numbers 1 to 3 without spaces

C. Prints each number 1, 2, and 3 on a new line

D. Causes an error because of the loop

Solution

1. Step 1: Understand the for loop over a list

   The loop goes through each element in the list [1, 2, 3] one by one.

2. Step 2: Print each element during iteration

   Each element (1, then 2, then 3) is printed on its own line because of the print statement.

3. Final Answer:

   Prints each number 1, 2, and 3 on a new line -> Option C

4. Quick Check:

   Loop prints items one by one [OK]

Hint: For loops print each list item separately [OK]

Common Mistakes:

• Thinking it prints the whole list at once
• Expecting numbers to print on the same line
• Confusing loop variable with list itself

2. Which of these is the correct syntax to loop over a list named fruits?

easy

A. for fruit in fruits:
print(fruit)

B. for fruits in fruit:
print(fruits)

C. loop fruit in fruits:
print(fruit)

D. for fruit to fruits:
print(fruit)

Solution

1. Step 1: Identify correct for loop syntax

   The correct Python syntax uses 'for variable in list:' to loop over items.

2. Step 2: Check each option

   for fruit in fruits: print(fruit) uses 'for fruit in fruits:', which is correct. Others use invalid keywords or reversed names.

3. Final Answer:

   for fruit in fruits: print(fruit) -> Option A

4. Quick Check:

   Use 'for item in list:' syntax [OK]

Hint: Remember: for variable in list: [OK]

Common Mistakes:

• Swapping variable and list names
• Using wrong keywords like 'loop' or 'to'
• Missing colon after for statement

3. What is the output of this code?

numbers = [2, 4, 6]
sum = 0
for n in numbers:
    sum += n
print(sum)

medium

A. 12

B. 0

C. 246

D. Error

Solution

1. Step 1: Understand the loop adding numbers

   The loop adds each number in the list [2, 4, 6] to sum, starting from 0.

2. Step 2: Calculate the total sum

   sum = 0 + 2 + 4 + 6 = 12

3. Final Answer:

   12 -> Option A

4. Quick Check:

   Sum of list items = 12 [OK]

Hint: Add each item inside the loop to get total [OK]

Common Mistakes:

• Printing sum before loop
• Concatenating numbers as strings
• Forgetting to initialize sum to 0

4. Find the error in this code:

items = [10, 20, 30]
for i in items
    print(i)

medium

A. List name is incorrect

B. Wrong variable name in loop

C. Indentation error in print

D. Missing colon after for statement

Solution

1. Step 1: Check for syntax errors in for loop

   The for loop must end with a colon ':' to be valid syntax.

2. Step 2: Identify missing colon

   The code misses ':' after 'for i in items', causing a syntax error.

3. Final Answer:

   Missing colon after for statement -> Option D

4. Quick Check:

   For loops need ':' at end [OK]

Hint: Always put ':' after for loop header [OK]

Common Mistakes:

• Forgetting colon after for statement
• Using wrong variable names
• Incorrect indentation of print

5. You have a list of lists: data = [[1, 2], [3, 4], [5, 6]]. How do you print all numbers one by one using iteration?

hard

A. print(data[0][0], data[1][1], data[2][2])

B. for sublist in data:
for num in sublist:
print(num)

C. for i in range(len(data)):
print(data[i])

D. for num in data:
print(num)

Solution

1. Step 1: Understand nested lists and iteration

   Each item in data is a list itself, so we need two loops: one for each sublist, one for numbers inside.

2. Step 2: Use nested for loops to access all numbers

   The outer loop goes through each sublist, the inner loop prints each number inside that sublist.

3. Final Answer:

   for sublist in data: for num in sublist: print(num) -> Option B

4. Quick Check:

   Nested loops print all inner items [OK]

Hint: Use nested loops for lists inside lists [OK]

Common Mistakes:

• Trying to print sublists directly
• Using single loop only
• Accessing wrong indexes causing errors