Day 17/100: Built-in Python Functions You Should Know

Welcome to Day 17 of the 100 Days of Python series!
Python comes packed with a set of powerful, ready-to-use tools known as built-in functions. These functions can save you time, simplify your code, and help you do everything from basic calculations to working with data types — no need to import anything!

Let’s explore some of the most useful built-in functions every Python developer should know.

📦 What You’ll Learn

• What built-in functions are
• Top 20+ built-in functions and how to use them
• Real-world use cases
• Bonus: how to discover more functions

🤔 What Are Built-in Functions?

Built-in functions are predefined functions that are always available in Python. You can use them anytime without importing a module.

Example:

print("Hello, Python!") # ✅ print is a built-in function 

🚀 Most Common Built-in Functions (with Examples)

1. print() – Display output

print("Learning Python!") 

2. len() – Get the length of a string, list, etc.

name = "Python" print(len(name)) # Output: 6 

3. type() – Find out the data type

print(type(5)) # <class 'int'> print(type("Hello")) # <class 'str'> 

4. int(), float(), str() – Type casting

age = "25" print(int(age)) # Converts string to integer 

5. input() – Take user input

name = input("Enter your name: ") print("Hello,", name) 

6. sum() – Add all items in an iterable

numbers = [10, 20, 30] print(sum(numbers)) # Output: 60 

7. max() / min() – Get highest/lowest value

print(max([3, 6, 2])) # 6 print(min([3, 6, 2])) # 2 

8. sorted() – Return a sorted list

print(sorted([5, 2, 9])) # [2, 5, 9] 

9. range() – Generate a sequence of numbers

for i in range(3): print(i) # 0, 1, 2 

10. enumerate() – Get index while looping

colors = ["red", "blue", "green"] for index, color in enumerate(colors): print(index, color) 

11. zip() – Combine iterables element-wise

names = ["Alice", "Bob"] scores = [85, 92] for name, score in zip(names, scores): print(f"{name} scored {score}") 

12. abs() – Absolute value

print(abs(-7)) # 7 

13. round() – Round a number

print(round(3.14159, 2)) # 3.14 

14. all() / any() – Test multiple conditions

print(all([True, True, False])) # False print(any([False, False, True])) # True 

15. dir() – Show attributes/methods of an object

print(dir(str)) # Shows all string methods 

16. help() – Get documentation

help(len) # Shows how len() works 

17. eval() – Execute a string as Python code (⚠️ use with caution)

expression = "3 + 5" print(eval(expression)) # Output: 8 

18. reversed() – Reverse an iterable

for char in reversed("Python"): print(char, end="") # nohtyP 

19. isinstance() – Check if a variable is of a type

x = 10 print(isinstance(x, int)) # True 

20. map() / filter() – Functional programming helpers

nums = [1, 2, 3] squared = list(map(lambda x: x**2, nums)) print(squared) # [1, 4, 9]  evens = list(filter(lambda x: x % 2 == 0, nums)) print(evens) # [2] 

💡 Bonus Tip: Explore All Built-in Functions

Use this to see all available built-in functions:

print(dir(__builtins__)) 

🧠 Recap

Today you learned:

• What built-in functions are
• 20+ of the most commonly used ones
• How to use them to write cleaner, faster code
• Where to find documentation using help() and dir()