Python me Lambda Function kya hota hai?

Lambda function ek anonymous function hai — yaani bina naam ka function. Isko ek hi line me likha ja sakta hai. Yeh tab useful hota hai jab aapko chhota sa function sirf ek baar ya thodi der ke liye chahiye ho aur poora def likhna unnecessarily lamba lage.

Lambda ki 3 main khasiyatein hain :-

Anonymous — naam nahi hota (usually)
One-liner — sirf ek expression likh sakte hain
Auto return — return likhna nahi padta, automatically return hota hai

Is page me yeh sab sikhenge :-

1. Lambda syntax aur basics
2. Lambda vs def
3. Lambda ke saath map()
4. Lambda ke saath filter()
5. Lambda ke saath reduce()
6. Lambda ke saath sorted()
7. Lambda as function argument

1. Lambda Syntax aur Basics

Lambda ka syntax bahut simple hai — lambda keyword, phir parameters, phir colon (:), phir expression (jo automatically return hota hai).

Syntax
lambda parameters : expression # Example: lambda x : x * 2

Example 1: Basic lambda — ek aur do parameters

Python

In [1]:

double = lambda x: x * 2
square = lambda x: x ** 2
add    = lambda a, b: a + b
greet  = lambda name: f"Namaste, {name}!"

print(double(5))
print(square(7))
print(add(10, 25))
print(greet("Rahul"))

Output

Example 2: Lambda seedha call karna (IIFE)

Python

In [1]:

# Lambda ko define karte hi call karna
result = (lambda x, y: x + y)(15, 25)
print("15 + 25 =", result)

# Condition ke saath lambda (ternary)
even_odd = lambda n: "Even" if n % 2 == 0 else "Odd"
print(even_odd(8))
print(even_odd(7))

# Multiple arguments
multiply = lambda a, b, c: a * b * c
print(multiply(2, 3, 4))

Output

2. Lambda vs def — Kya Fark Hai?

Lambda aur def dono function banate hain, lekin dono ka use alag alag situation me hota hai.

Feature	def Function	Lambda Function
Naam	Hamesha hota hai	Usually nahi hota
Lines	Multiple lines	Sirf ek line
return	Explicitly likhna padta hai	Auto return
Statements	Koi bhi statement	Sirf ek expression
Use kab	Complex logic, reuse	Short, one-time use

Example 1: def aur lambda — same kaam alag tarike se

Python

In [1]:

# def se — 3 lines
def add_def(a, b):
    return a + b

# Lambda se — 1 line, same kaam!
add_lambda = lambda a, b: a + b

print("def result    :", add_def(10, 20))
print("lambda result :", add_lambda(10, 20))
print("Dono same hain:", add_def(5, 3) == add_lambda(5, 3))

Output

3. Lambda ke saath map()

map() ek function hai jo ek function aur iterable leta hai aur har element par woh function apply karta hai. Lambda ke saath yeh bahut concise aur powerful ho jaata hai.

Syntax
map(function, iterable) # Result list me convert karna padta hai: list(map(...))

Example 1: map() — har number ka square nikalna

Python

In [1]:

nums = [1, 2, 3, 4, 5]

# Har number ka square
squares = list(map(lambda x: x**2, nums))
print("Squares:", squares)

# Har number ko double karo
doubled = list(map(lambda x: x * 2, nums))
print("Doubled:", doubled)

# Celsius to Fahrenheit convert karo
celsius = [0, 20, 37, 100]
fahrenheit = list(map(lambda c: (c * 9/5) + 32, celsius))
print("Fahrenheit:", fahrenheit)

Output

Example 2: map() — strings pe apply karna

Python

In [1]:

names = ["rahul", "priya", "arjun", "neha"]

# Sabko title case me convert karo
titled = list(map(lambda s: s.title(), names))
print("Title case:", titled)

# Har naam ki length nikalo
lengths = list(map(lambda s: len(s), names))
print("Lengths:", lengths)

# Har naam ke saath greeting banana
greetings = list(map(lambda s: f"Hello {s.title()}!", names))
print("Greetings:", greetings)

Output

4. Lambda ke saath filter()

filter() ek function hai jo sirf wahi elements rakhta hai jiske liye function True return kare. Matlab ek condition ke hisaab se list filter karna.

Example 1: filter() — even numbers aur positive numbers

Python

In [1]:

nums = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

# Sirf even numbers
evens = list(filter(lambda x: x % 2 == 0, nums))
print("Evens:", evens)

# Sirf odd numbers
odds = list(filter(lambda x: x % 2 != 0, nums))
print("Odds:", odds)

# 5 se bade numbers
greater = list(filter(lambda x: x > 5, nums))
print("Greater than 5:", greater)

Output

Example 2: filter() — marks aur names filter karna

Python

In [1]:

marks = [85, 42, 91, 38, 76, 55, 29, 88]

# Pass (50+) aur fail students
passed = list(filter(lambda m: m >= 50, marks))
failed = list(filter(lambda m: m < 50, marks))
print("Passed:", passed)
print("Failed:", failed)

# Names filter — 5 se bade naam
names = ["Raj", "Priya", "Om", "Arjun", "Neha", "Sana", "Vikram"]
long_names = list(filter(lambda n: len(n) > 4, names))
print("Long names:", long_names)

Output

5. Lambda ke saath reduce()

reduce() list ke elements ko ek ek karke combine karta hai aur ek single value deta hai. Isko use karne ke liye functools module import karna padta hai.

Example 1: reduce() — product aur max nikalna

Python

In [1]:

from functools import reduce

nums = [1, 2, 3, 4, 5]

# Sum — ek ek karke jodna: ((((1+2)+3)+4)+5) = 15
total = reduce(lambda a, b: a + b, nums)
print("Sum:", total)

# Product — ek ek karke multiply: ((((1*2)*3)*4)*5) = 120
product = reduce(lambda a, b: a * b, nums)
print("Product:", product)

# Maximum — ek ek karke bada dhundhna
maximum = reduce(lambda a, b: a if a > b else b, nums)
print("Maximum:", maximum)

Output

Example 2: reduce() — strings ko join karna

Python

In [1]:

from functools import reduce

words = ["Python", "is", "awesome", "language"]

# Strings ko space ke saath jodna
sentence = reduce(lambda a, b: a + " " + b, words)
print("Sentence:", sentence)

# Longest word dhundhna
longest = reduce(lambda a, b: a if len(a) >= len(b) else b, words)
print("Longest word:", longest)

Output

6. Lambda ke saath sorted()

sorted() me key parameter hota hai jisme lambda deke custom sorting kar sakte hain — kisi bhi field se, kisi bhi order me.

Example 1: List of numbers — custom sorting

Python

In [1]:

nums = [5, -3, 8, -1, 2, -7, 4]

# Normal sort
print("Normal sort:", sorted(nums))

# Absolute value se sort (negative ignore karke)
print("By abs value:", sorted(nums, key=lambda x: abs(x)))

# Descending order
print("Descending  :", sorted(nums, reverse=True))

# Strings — length se sort
words = ["banana", "kiwi", "apple", "fig", "mango"]
print("By length:", sorted(words, key=lambda w: len(w)))

Output

Example 2: List of dictionaries sort karna — key se

Python

In [1]:

students = [
    {"name": "Arjun", "marks": 78},
    {"name": "Priya", "marks": 92},
    {"name": "Rahul", "marks": 65},
    {"name": "Neha",  "marks": 88}
]

# Marks se sort — ascending
by_marks = sorted(students, key=lambda s: s["marks"])
print("By marks (asc):")
for s in by_marks:
    print(f"  {s['name']}: {s['marks']}")

# Marks se sort — descending (topper pehle)
by_marks_desc = sorted(students, key=lambda s: s["marks"], reverse=True)
print("\nBy marks (topper first):")
for s in by_marks_desc:
    print(f"  {s['name']}: {s['marks']}")

Output

7. Lambda as Function Argument

Lambda ka sabse popular use — kisi function ko argument ke roop me dena. Isko higher-order functions kehte hain.

Example 1: Function jo dusri function leta hai (higher-order)

Python

In [1]:

def apply_operation(nums, operation):
    return [operation(n) for n in nums]

numbers = [1, 2, 3, 4, 5]

# Alag alag operations lambda se pass karo
print(apply_operation(numbers, lambda x: x ** 2))    # squares
print(apply_operation(numbers, lambda x: x * 3))     # triple
print(apply_operation(numbers, lambda x: x + 100))   # add 100

Output

Example 2: map, filter, reduce — teeno ek saath

Python

In [1]:

from functools import reduce

marks = [45, 82, 91, 38, 76, 55, 29, 88, 62, 95]

# Step 1: filter — sirf pass wale (50+)
passed = list(filter(lambda m: m >= 50, marks))
print("Passed:", passed)

# Step 2: map — unke squares nikalo (bonus marks ke liye)
bonus = list(map(lambda m: round(m * 1.1, 1), passed))
print("With 10% bonus:", bonus)

# Step 3: reduce — total nikalo
total = reduce(lambda a, b: a + b, bonus)
print("Total bonus marks:", round(total, 1))

Output

Quick Summary — Lambda aur Functions ek nazar me

Concept	Kaam	Example
lambda	Anonymous ek-line function	lambda x: x*2
Multiple params	Do ya zyada parameters	lambda a,b: a+b
Condition	Ternary expression	lambda x: "E" if x%2==0 else "O"
map()	Har element pe function apply	map(lambda x: x**2, lst)
filter()	Condition se filter karo	filter(lambda x: x>5, lst)
reduce()	Ek value me combine karo	reduce(lambda a,b: a+b, lst)
sorted() key	Custom sort order	sorted(lst, key=lambda x: x[1])
Higher-order	Function ko argument me do	apply(lst, lambda x: x*2)

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