Python - Loop Arrays (Complete Guide for Beginners)

 In Python, arrays are used to store multiple values of the same data type. One of the most important operations when working with arrays is looping through elements.

Looping allows you to access each item in the array one by one, making it useful for processing data, calculations, and filtering values.

In this tutorial, you will learn different ways to loop through arrays in Python with clear examples.

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Creating an Array

We use Python’s array module.

import array as arr

numbers = arr.array('i', [10, 20, 30, 40, 50])
print(numbers)

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1. Loop Through Array Using for Loop

The simplest way to loop through an array is using a for loop.

Example

for num in numbers:
    print(num)

Output

10
20
30
40
50

Explanation

• Each element is accessed one by one
• No need to use index manually

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2. Loop Using Index (range + len)

You can also loop using index positions.

Example

for i in range(len(numbers)):
    print(numbers[i])

Output

10
20
30
40
50

Explanation

• range(len(numbers)) generates index values
• Useful when you need index positions

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3. Loop Using while Loop

Example

i = 0

while i < len(numbers):
    print(numbers[i])
    i += 1

Output

10
20
30
40
50

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4. Loop with Condition (Filter Values)

You can loop and filter values at the same time.

Example: Print values greater than 25

for num in numbers:
    if num > 25:
        print(num)

Output

30
40
50

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5. Loop and Modify Values

You can process each item during looping.

Example: Multiply each element by 2

for num in numbers:
    print(num * 2)

Output

20
40
60
80
100

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6. Loop Using Index for Modification

To modify an array, use index-based loop.

Example

for i in range(len(numbers)):
    numbers[i] = numbers[i] + 5

print(numbers)

Output

array('i', [15, 25, 35, 45, 55])

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7. Loop Using enumerate (Advanced)

Although arrays don’t directly use enumerate like lists, you can convert them.

Example

for index, value in enumerate(numbers):
    print(index, value)

Output

0 15
1 25
2 35
3 45
4 55

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Real-World Example: Student Marks

import array as arr

marks = arr.array('i', [85, 90, 78, 88])

total = 0

for mark in marks:
    total += mark

print("Total Marks:", total)

Output

Total Marks: 341

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Real-World Example: Product Prices

import array as arr

prices = arr.array('f', [99.99, 149.50, 200.75])

for price in prices:
    print("Price:", price)

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Loop Types Summary

Method	Description
for loop	Direct element access
range + len	Index-based looping
while loop	Manual control loop
condition loop	Filter values
modify loop	Change elements

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Common Mistakes

Mistake 1: Infinite While Loop

❌ Wrong:

i = 0
while i < len(numbers):
    print(numbers[i])

✔ Missing increment causes infinite loop

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Mistake 2: Modifying Array While Iterating

for num in numbers:
    numbers.remove(num)

✔ This may skip elements or cause errors

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Mistake 3: Wrong Index Access

print(numbers[10])

✔ Causes IndexError

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Safe Loop Example

for num in numbers[:]:
    print(num)

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Array Loop Methods Summary

Method	Use
for loop	Simple iteration
while loop	Controlled iteration
index loop	Position-based access
condition loop	Filtering
modify loop	Updating values

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Practice Exercise 1

Print all even numbers from an array.

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Practice Exercise 2

Multiply each element by 3 and print results.

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Conclusion

Looping arrays in Python is a fundamental skill for working with data.

You learned:

• Different ways to loop arrays
• How to use for, while, and index-based loops
• How to filter and modify array values
• Real-world examples

Mastering array loops is essential for data processing, analytics, and programming logic building.