How does the Python's range function work?

Python’s range() function is used to generate a sequence of numbers — typically for loops, iterations, and indexing tasks. What’s interesting is that range() doesn’t actually create a full list of numbers in memory. Instead, it produces a lazy sequence (an immutable and efficient range object) that generates values on demand.

 Basic Usage

range() can take 1, 2, or 3 arguments:

• range(stop) → numbers from 0 to stop - 1
  
• range(start, stop) → numbers from start to stop - 1
  
• range(start, stop, step) → numbers with increments/decrements based on step
  

Example:

for i in range(2, 10, 2):
    print(i)
Output: 2 4 6 8

 Key Features

It does not store all numbers at once — memory efficient

You can convert it to a list if needed:

   list(range(5))  # [0, 1, 2, 3, 4]

It supports negative steps, allowing reverse loops

It is an immutable sequence type

 Why is range() efficient?

It calculates each value only when needed, not ahead of time

Works great for large ranges, for example:

   range(1_000_000_000)

 This won’t crash your system because the numbers aren’t all stored

In simple words, range() is a smart way for Python to generate sequences efficiently, making loops faster and memory usage much lower compared to actual lists.