🏷️ Understanding lambda Functions in Python

A lambda function is a small anonymous function (i.e., a function without a name) that is typically used for short, simple operations. It is also called a “lambda expression”.

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🎯 Basic Syntax

lambda arguments: expression

• lambda is the keyword.
• arguments are input values, similar to parameters in a normal function.
• expression is the operation that will be performed and returned.

👉 Example (Basic Addition)

add = lambda x, y: x + y
print(add(2, 3))  # Output: 5

📌 How does it work?

• lambda x, y: x + y → Defines a function that takes x and y as arguments and returns their sum.
• add(2, 3) → Calls the lambda function with arguments 2 and 3.

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🔥 Why Use Lambda Functions?

• Concise & Readable: They are one-liners.
• Used Inside Other Functions: Often used when you need a quick function inside another function.
• No Need for def: Saves time when defining small functions.

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⚡ Examples & Use Cases

✅ 1. Using lambda in map()

📌 map() applies a function to each item in an iterable.

nums = [1, 2, 3, 4]
squared = list(map(lambda x: x ** 2, nums))
print(squared)  # Output: [1, 4, 9, 16]

Equivalent with def:

def square(x):
    return x ** 2
 
squared = list(map(square, nums))

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✅ 2. Using lambda in filter()

📌 filter() keeps values that return True.

nums = [1, 2, 3, 4, 5, 6]
evens = list(filter(lambda x: x % 2 == 0, nums))
print(evens)  # Output: [2, 4, 6]

Equivalent with def:

def is_even(x):
    return x % 2 == 0
 
evens = list(filter(is_even, nums))

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✅ 3. Using lambda in sorted()

📌 Custom sorting with lambda

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)]

🔍 Explanation:

• key=lambda x: x[1] → Sorts by the second element (age).

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✅ 4. Using lambda in pandas

📌 Applying operations on DataFrame columns

import pandas as pd
 
df = pd.DataFrame({'A': [1, 2, 3, 4]})
df['B'] = df['A'].apply(lambda x: x * 2)
print(df)

Output:

   A  B
0  1  2
1  2  4
2  3  6
3  4  8

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⚠️ When NOT to Use lambda

• If the function logic is complex → Use def instead.
• If the function is reusable → Named functions are better.

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🎯 Key Takeaways

✅ lambda creates small anonymous functions.
✅ Best used for short, one-time operations.
✅ Commonly used in map(), filter(), sorted(), and pandas.
✅ If the function gets complex, use def instead.