How to Iterate Through a List in Python

What you’ll build or solve

You’ll loop through a Python list and do something with each item, like print it, transform it, or filter it.

When this approach works best

Iterating through a list works well when you:

• Process each item in a dataset, like names, file paths, or API results.
• Transform values, like converting strings to numbers or normalizing text.
• Filter items, like keeping only valid entries or removing duplicates.

Skip this approach when you can use built-in functions that already express your goal, like sum(), any(), or a list comprehension for simple transforms. Those are often shorter and easier to read.

Prerequisites

• Python 3 installed
• You know what a list is

Step-by-step instructions

1) Loop through items with for

A for loop is the most common way to iterate through a list.

names= ["Amina","Luka","Noor"]

fornameinnames:
print(name)

What to look for: The loop variable (name) takes on each value from the list, one at a time.

2) Get the index and the item

Use enumerate() when you need both the position and the value.

names= ["Amina","Luka","Noor"]

fori,nameinenumerate(names):
print(i,name)

If you want human-friendly numbering, start at 1.

names= ["Amina","Luka","Noor"]

fori,nameinenumerate(names,start=1):
print(i,name)

What to look for: enumerate(..., start=1) changes the first index from 0 to 1.

3) Iterate with a condition or transformation

If you’re building a new list, iterate and collect results.

Option A (common): list comprehension

scores= [10,0,25,30]
non_zero= [sforsinscoresifs!=0]

print(non_zero)

Option B: for loop with append() when you need more logic

scores= [10,0,25,30]
non_zero= []

forsinscores:
ifs!=0:
non_zero.append(s)

print(non_zero)

What to look for: List comprehensions work best for simple transforms or filters. Use a for loop when you need multiple steps or more complex logic.

Examples you can copy

Example 1: Transform each item

words= ["  apple ","Banana","CHERRY"]
cleaned= [w.strip().lower()forwinwords]

print(cleaned)

Example 2: Build a dictionary from a list

names= ["Amina","Luka","Noor"]
name_to_len= {}

fornameinnames:
name_to_len[name]=len(name)

print(name_to_len)

Example 3: Filter out empty values

items= ["ok","","  ","valid"]
filtered= [xforxinitemsifx.strip()]

print(filtered)

Example 4: Stop early when you find a match

numbers= [3,8,12,7,5]

forninnumbers:
ifn%2==0:
first_even=n
break
else:
first_even=None

print(first_even)

What to look for: The else block runs only if the loop doesn’t hit break.

Example 5: Iterate over two lists at once

names= ["Amina","Luka","Noor"]
scores= [42,38,50]

forname,scoreinzip(names,scores):
print(name,score)

What to look for: zip() stops at the shortest list. If lengths can differ, decide how you want to handle extra items.

Common mistakes and how to fix them

Mistake 1: Modifying a list while iterating over it

What you might do:

nums= [1,2,3,4]

forninnums:
ifn%2==0:
nums.remove(n)

Why it breaks: Removing items shifts the remaining elements, so you can skip values.

Correct approach: Create a new list instead.

nums= [1,2,3,4]
nums= [nforninnumsifn%2!=0]

print(nums)

Mistake 2: Using range(len(list)) when you don’t need indexes

What you might do:

names= ["Amina","Luka","Noor"]

foriinrange(len(names)):
print(names[i])

Why it breaks: It’s easy to make off-by-one mistakes, and the code is harder to read than a direct loop.

Correct approach:

names= ["Amina","Luka","Noor"]

fornameinnames:
print(name)

If you need indexes, use enumerate():

fori,nameinenumerate(names):
print(i,name)

Mistake 3: Forgetting break and doing extra work

What you might do:

numbers= [3,8,12,7,5]
first_even=None

forninnumbers:
ifn%2==0:
first_even=n

Why it breaks: You keep looping, so you end up with the last even number, not the first one.

Correct approach:

numbers= [3,8,12,7,5]
first_even=None

forninnumbers:
ifn%2==0:
first_even=n
break

Troubleshooting

If you see TypeError: 'int' object is not iterable, you’re looping over a single value, not a list. Print the variable and confirm it’s a list.

If your loop misses items, you might be changing the list while iterating. Filter into a new list instead.

If you get IndexError, check if you used indexes like names[i] with a bad range. Prefer for item in items or enumerate().

If nothing prints, confirm the list isn’t empty and confirm your code block actually runs.

Quick recap

• Use for item in items for the most readable list iteration.
• Use enumerate(items) when you need indexes.
• Use a list comprehension for simple filtering or transformation.
• Avoid mutating a list while iterating over it.
• Use break when you want to stop after finding what you need.