Python Lambda function
Table of Contents
Description
A lambda function in Python is a small anonymous function defined using the lambda keyword. It can take any number of arguments, but can only have one expression. It's commonly used for short, throwaway functions especially in functional programming scenarios like map(), filter(), and sorted().
Prerequisites
- Knowledge of basic functions
- Familiarity with expressions
- Understanding of higher-order functions like map(), filter(), etc.
Examples
Here's a simple program in Python:
✅ Basic Lambda Function
# A simple lambda function that adds 10 to a number
add_ten = lambda x: x + 10
print(add_ten(5)) # Output: 15
✅ Lambda with Multiple Arguments
# Lambda to multiply two numbers
multiply = lambda a, b: a * b
print(multiply(4, 5)) # Output: 20
✅ Using Lambda with map()
# Doubles each number in the list
nums = [1, 2, 3, 4]
doubled = list(map(lambda x: x * 2, nums))
print(doubled) # Output: [2, 4, 6, 8]
✅ Using Lambda with filter()
# Filters even numbers from the list
even_nums = list(filter(lambda x: x % 2 == 0, nums))
print(even_nums) # Output: [2, 4]
✅ Lambda in sorted() with key
# Sorts a list of tuples based on the second element
pairs = [(1, 4), (2, 1), (3, 9)]
sorted_pairs = sorted(pairs, key=lambda x: x[1])
print(sorted_pairs) # Output: [(2, 1), (1, 4), (3, 9)]
Real-World Applications
Used in data transformation pipelines
Simplifies callback functions in GUI or web development
Helps sort or filter complex datasets on the fly
Widely used in pandas and NumPy for inline operations
Common in AI/ML pipelines for inline feature transformations
Where topic Can Be Applied
Data Science: Inline transformations in pandas, NumPy
Web Development: Inline route functions or conditions
Automation Scripts: Quick filtering/mapping without extra function definitions
Machine Learning: Lambda used in data preprocessing
Functional Programming: Combined with map(), reduce(), etc.
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Interview Questions
What is a lambda function in Python?
How is a lambda function different from a normal function?
Can lambda functions have multiple expressions?
Where would you use a lambda over a def function?
How can you use lambda with map(), filter(), or sorted()?