List comprehension with condition in Python - Mini Project: Build & Apply

List comprehension with condition

📖 Scenario: You are working in a fruit store. You have a list of fruit names, but you only want to select the fruits that have more than 5 letters in their names.

🎯 Goal: Build a Python program that uses list comprehension with a condition to create a new list containing only the fruits with names longer than 5 letters.

📋 What You'll Learn

Create a list called fruits with the exact values: 'apple', 'banana', 'kiwi', 'mango', 'pineapple', 'pear'

Create a variable called min_length and set it to 5

Use a list comprehension with a condition to create a new list called long_fruits that contains only fruits with length greater than min_length

Print the long_fruits list

💡 Why This Matters

🌍 Real World

Filtering lists based on conditions is common in data processing, like selecting products, names, or records that meet certain criteria.

💼 Career

Understanding list comprehension with conditions helps in writing clean and efficient code for data analysis, web development, and automation tasks.

1

Create the initial list of fruits

Create a list called fruits with these exact values: 'apple', 'banana', 'kiwi', 'mango', 'pineapple', 'pear'

Python

# Create the list called fruits with the given fruit names
# Your code here

Hint

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

2

Set the minimum length for fruit names

Create a variable called min_length and set it to the number 5

Python

fruits = ['apple', 'banana', 'kiwi', 'mango', 'pineapple', 'pear']
# Create the variable min_length and set it to 5
# Your code here

Hint

Use the equals sign = to assign the value 5 to the variable min_length.

3

Use list comprehension with condition

Use a list comprehension with a condition to create a new list called long_fruits that contains only fruits from fruits whose length is greater than min_length

Python

fruits = ['apple', 'banana', 'kiwi', 'mango', 'pineapple', 'pear']
min_length = 5
# Create long_fruits using list comprehension with condition
# Your code here

Hint

Use the syntax: [item for item in list if condition] to filter items.

4

Print the filtered list

Write a print statement to display the long_fruits list

Python

fruits = ['apple', 'banana', 'kiwi', 'mango', 'pineapple', 'pear']
min_length = 5
long_fruits = [fruit for fruit in fruits if len(fruit) > min_length]
# Print the long_fruits list
# Your code here

Hint

Use print(long_fruits) to show the result.

Practice

1. What does the following list comprehension do?
[x for x in range(5) if x % 2 == 0]

easy

A. Creates a list of odd numbers from 0 to 4

B. Creates a list of even numbers from 0 to 4

C. Creates a list of numbers from 1 to 5

D. Creates a list of numbers divisible by 3

Solution

1. Step 1: Understand the range and condition

   The range(5) generates numbers 0, 1, 2, 3, 4. The condition x % 2 == 0 selects numbers divisible by 2 (even numbers).

2. Step 2: Apply the condition to each number

   From 0 to 4, the even numbers are 0, 2, and 4. These are included in the new list.

3. Final Answer:

   [0, 2, 4] -> Option B

4. Quick Check:

   Even numbers from 0 to 4 = [0, 2, 4] [OK]

Hint: Look for the condition after 'if' to filter items [OK]

Common Mistakes:

• Confusing even and odd numbers
• Ignoring the condition and taking all numbers
• Misunderstanding the range function

2. Which of the following is the correct syntax for a list comprehension that selects numbers greater than 10 from list nums?

easy

A. [x for x > 10 in nums]

B. [x if x > 10 for x in nums]

C. [if x > 10 for x in nums]

D. [x for x in nums if x > 10]

Solution

1. Step 1: Recall list comprehension syntax

   The correct syntax is [expression for item in iterable if condition]. Here, expression and item are both x, iterable is nums, and condition is x > 10.

2. Step 2: Check each option

   [x for x in nums if x > 10] matches the correct syntax. The other options have misplaced or missing parts.

3. Final Answer:

   [x for x in nums if x > 10] -> Option D

4. Quick Check:

   Correct list comprehension syntax = [x for x in nums if x > 10] [OK]

Hint: Remember: for comes before if in list comprehension [OK]

Common Mistakes:

• Placing 'if' before 'for'
• Omitting 'for' keyword
• Using incorrect order of clauses

3. What is the output of this code?

nums = [3, 7, 12, 5, 20]
result = [n*2 for n in nums if n > 6]
print(result)

medium

A. [14, 24, 40]

B. [3, 7, 12, 5, 20]

C. [6, 14, 24, 10, 40]

D. [12, 24, 40]

Solution

1. Step 1: Identify numbers greater than 6

   From the list, numbers greater than 6 are 7, 12, and 20.

2. Step 2: Multiply each selected number by 2

   7*2=14, 12*2=24, 20*2=40. These form the new list.

3. Final Answer:

   [14, 24, 40] -> Option A

4. Quick Check:

   Filter >6 and double = [14, 24, 40] [OK]

Hint: Apply condition first, then transform each item [OK]

Common Mistakes:

• Multiplying all numbers, ignoring condition
• Including numbers less than or equal to 6
• Confusing multiplication with addition

4. Find the error in this list comprehension:

values = [1, 2, 3, 4]
new_values = [x for x in values if x > 2 else 0]

medium

A. SyntaxError due to incorrect use of else in list comprehension

B. No error, code runs fine

C. TypeError because of wrong condition

D. NameError because x is undefined

Solution

1. Step 1: Understand list comprehension with condition

   In list comprehension, 'if' can be used to filter items, but 'else' must be part of a conditional expression, not after 'if' alone.

2. Step 2: Identify the syntax error

   The code uses 'if x > 2 else 0' incorrectly. The correct way is to use a conditional expression inside the expression part, like [x if x > 2 else 0 for x in values].

3. Final Answer:

   SyntaxError due to incorrect use of else in list comprehension -> Option A

4. Quick Check:

   Else must be inside expression, not after if clause [OK]

Hint: Use if-else inside expression, not after if clause [OK]

Common Mistakes:

• Placing else after if in list comprehension filter
• Confusing filter condition with conditional expression
• Ignoring Python syntax rules for comprehensions

5. You have a list of strings: words = ['apple', '', 'banana', 'cherry', '', 'date']. Which list comprehension creates a new list with only non-empty strings in uppercase?

hard

A. [w for w in words if w.upper()]

B. [w.upper() if w else w for w in words]

C. [w.upper() for w in words if w]

D. [w.upper() for w in words if w == '']

Solution

1. Step 1: Understand filtering non-empty strings

   In Python, empty strings are false in boolean context. Using if w filters out empty strings.

2. Step 2: Convert filtered strings to uppercase

   For each non-empty string w, w.upper() converts it to uppercase.

3. Final Answer:

   [w.upper() for w in words if w] -> Option C

4. Quick Check:

   Filter non-empty and uppercase = [w.upper() for w in words if w] [OK]

Hint: Use 'if w' to filter non-empty strings in list comprehension [OK]

Common Mistakes:

• Filtering empty strings incorrectly
• Using if-else incorrectly inside comprehension
• Not converting strings to uppercase