A lambda function in Python is a small, anonymous function defined using the lambda keyword. It can take multiple arguments but must have only one expression. Lambda functions are useful for short, simple operations where defining a full function is unnecessary.
1. Syntax of a Lambda Function
pythonCopyEditlambda arguments: expression
lambda: The keyword used to define a lambda function.arguments: One or more inputs, similar to function parameters.expression: A single expression evaluated and returned (no multiple statements allowed).
2. Basic Example of a Lambda Function
Example: Lambda Function to Add Two Numbers
add = lambda x, y: x + y
print(add(3, 5))
Output:
8
- Here,
lambda x, y: x + yis equivalent to: pythonCopyEditdef add(x, y): return x + y
3. Lambda Function with One Argument
square = lambda x: x * x
print(square(4))
Output:
16
4. Using Lambda Functions with map()
The map() function applies a function to all items in an iterable.
Example: Squaring a List of Numbers
numbers = [1, 2, 3, 4, 5]
squared = list(map(lambda x: x * x, numbers))
print(squared)
Output:
[1, 4, 9, 16, 25]
5. Using Lambda Functions with filter()
The filter() function filters elements based on a condition.
Example: Filtering Even Numbers
numbers = [1, 2, 3, 4, 5, 6]
evens = list(filter(lambda x: x % 2 == 0, numbers))
print(evens)
Output:
[2, 4, 6]
6. Using Lambda Functions with sorted()
The sorted() function can use a lambda function as a sorting key.
Example: Sorting a List of Tuples by Second Element
students = [("Alice", 25), ("Bob", 20), ("Charlie", 23)]
sorted_students = sorted(students, key=lambda x: x[1])
print(sorted_students)
Output:
[('Bob', 20), ('Charlie', 23), ('Alice', 25)]
7. Using Lambda Functions Inside Another Function
Example: Multiplication Function with Lambda
def multiplier(n):
return lambda x: x * n
double = multiplier(2)
print(double(5))
Output:
10
multiplier(2)returnslambda x: x * 2, makingdouble(5)equal to5 * 2 = 10.
8. Lambda Function with reduce()
The reduce() function (from functools) applies a function cumulatively.
Example: Summing a List of Numbers
from functools import reduce
numbers = [1, 2, 3, 4, 5]
sum_result = reduce(lambda x, y: x + y, numbers)
print(sum_result)
Output:
15
9. Comparison Between Lambda and Normal Functions
Regular Function
def cube(x):
return x ** 3
print(cube(3))
Lambda Equivalent
cube = lambda x: x ** 3
print(cube(3))
Both produce:
27
10. Limitations of Lambda Functions
- Can only have one expression (no multiple statements).
- Limited readability for complex logic.
- Cannot contain
return, loops, or assignments.