Summary  
This chapter introduces Python’s built-in functions—such as print, min, max, abs, round, and pow—that provide common operations out of the box, enabling you to perform tasks like finding extremes or rounding numbers without implementing the logic yourself.

General domain of usage  
Data analysis

**Built-in functions** in Python are predefined and available for use without any additional setup. One example is the `print()` function, which you have already used. You do not need to define it, write its body, or specify its return value, you simply call it and provide inputs.

Many more functions exist. Imagine you have to find the largest number within the list. With what you've learned, you could write a loop that compares each element to the current largest value, updating it when a bigger number is found. Fortunately, Python provides built-in functions that make this task easier and efficient.

For example, if we need to calculate the **population density** for a set of countries in the `countries` list, we simply divide the **population** by the **land area**.  


# Initial data
countries = [["USA", 9629091, 331002651],
             ["Germany", 357114, 83783942],
             ["India", 3166391, 1380004385]]

# Iterating over external list
for i in range(len(countries)):
    if type(countries[i]) is list:
        # Computing population density for a country
        pop_dens = countries[i][2]/countries[i][1]
        print(countries[i][0], pop_dens, 'people per km²')

The list contained five nested sub-lists. A loop iterated through the main list, checking if each item was a list. If so, the population density was calculated by dividing the third item (population) by the second item (area).

# Initial data
countries = [["USA", 9629091, 331002651],
            ["Germany", 357114, 83783942],
            ["India", 3166391, 1380004385]]

# Iterating over external list
for i in range(len(countries)):
    if type(countries[i]) is list:
        # Computing population density for a country
        pop_dens = round(countries[i][2]/countries[i][1], 2)
        print(countries[i][0], pop_dens, 'people per km²')

However, the results were difficult to read due to **more than 10 decimal places**. To improve readability, you can use the `round()` function to limit the output to **2 decimal places**. This function takes **two arguments**: the first is the number to be rounded, and the second specifies the number of decimal places to retain.

Which function would you use to round a number to a specific number of decimal places?

Gain a solid understanding of how functions shape Python programming. Master defining and calling functions, working with arguments, handling return values, and creating flexible, efficient code using recursion and lambda expressions.

Explore what functions are and why they're essential in Python. Learn how to create functions, define arguments, handle return values, and use built-in functions effectively.

Built-In Functions in Python