Python - Loop Through a Range

Looping through a range is an important operation in Python. In this article, we will explore the different ways to loop through a range in Python, demonstrating how we customize start, end, and step values, as well as alternative methods for more advanced use cases like looping through floating-point ranges or infinite sequences.

Example of Using range()

The most simple way to loop through a range in Python is by using the range() function in a for loop. By default, the range() function generates numbers starting from 0 up to, but not including, the specified endpoint.

# Loop from 0 to 4
for i in range(5):
    print(i, end=" ") 

0 1 2 3 4 

Explanation:

• Here only one argument is provided so the range begins at 0.
• The range ends at n-1 i.e. 4, where n is the argument provided.

Let's see some more methods and see how we can loop through a range in Python.

Using Start and Step Value in range()

In Python, we can loop through a range using the start parameter by leveraging the range() function. The range() function can take up to three parameters: start, stop, and step. Here’s the general syntax for using the start parameter in range():

range(start, stop, step)

• start: The value at which the range starts (inclusive).
• stop: The value at which the range stops (exclusive).
• step: The increment or decrement for each iteration (default is 1).

Example:

# Loop with a step value of 2
for i in range(0, 10, 2):
    print(i, end=" ") 

0 2 4 6 8 

Explanation:

1. The step value(2) determines how much the range increments after each iteration.
2. It supports both positive and negative step values for ascending or descending loops.

Note: Python also allows looping in reverse order by setting a negative step value in the range() function.

#Loop from 10 to 1 in reverse
for i in range(10, 0, -1):
print(i, end=" ") # Output: 10 9 8 7 6 5 4 3 2 1

Using enumerate() and range()

The enumerate() function, when combined with range(), provides both the index and the value during iteration.

# Loop with index and value
for idx, val in enumerate(range(5, 10)):
    print(f"Index: {idx}, Value: {val}")

Index: 0, Value: 5
Index: 1, Value: 6
Index: 2, Value: 7
Index: 3, Value: 8
Index: 4, Value: 9

Explanation:

1. enumerate() returns a tuple containing the index and the corresponding value in the range.
2. It works seamlessly with ranges of any size.

Looping Through Floating-Point Ranges

Since the range() function only supports integers, creating a range of floating-point numbers requires external libraries or custom solutions. Here we will use numpy.arrange().

import numpy as np
# Loop through floating-point numbers
for i in np.arange(0.5, 2.5, 0.5):
    print(i, end=" ") 

Explanation:

• Here, NumPy allows iteration over fractional ranges.
• It Supports precise step values for scientific or mathematical applications.

Using itertools.count() for Infinite Ranges

The itertools.count() function generates an infinite sequence of numbers, starting from a given value and stepping by a defined amount. It is suitable for dynamic or unpredictable iteration lengths, such as streaming data.

from itertools import count
# Infinite range with manual termination
for i in count(1, 3): 
    if i > 10:
        break
    print(i, end=" ")  

1 4 7 10 

Explanation:

• Here, it automatically continues until a stopping condition is provided.
• It supports both positive and negative step values.