How to Get Length of a List in Python

What you’ll build or solve

You’ll get the number of items in a Python list and use that number in real code.

When this approach works best

Getting the length of a list works well when you:

• Validate input, like checking a list of results before accessing items[0].
• Control loops, like stopping after N items or chunking data into batches.
• Compare lists, like confirming two lists have the same number of items before pairing them.

Skip this approach if you only need to loop over items. A for item in items loop doesn’t need the length and is usually easier to read.

Prerequisites

• Python 3 installed
• You know what a list is

Step-by-step instructions

1) Get the length with len()

Use len() to get the number of items in a list.

nums= [10,25,30]
count=len(nums)

print(count)

What to look for: len([]) returns 0, so empty lists won’t crash your code.

2) Use the length to check for an empty list

A quick length check helps you avoid IndexError when accessing elements.

Option A (most common): Use the list directly in a condition

items= []

ifitems:
first=items[0]
else:
first=None

print(first)

Option B: Compare len() to 0 for clarity

items= []

iflen(items)>0:
first=items[0]
else:
first=None

print(first)

What to look for: if items: is the standard Python pattern. Empty lists are treated as False.

3) Use the length safely with indexes

Valid indexes stop at len(items) - 1.

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

last_index=len(names)-1
last_name=names[last_index]

print(last_name)

What to look for: If the list might be empty, len(names) - 1 becomes -1. That’s a valid index in Python, but it means “last item,” so check for emptiness first when that matters.

Examples you can copy

Example 1: Guard before accessing the first item

results= ["match_1","match_2"]

ifresults:
print("First result:",results[0])
else:
print("No results")

Example 2: Take the last N items (or fewer)

items= ["a","b","c","d","e"]
n=3

start=max(len(items)-n,0)
tail=items[start:]

print(tail)

Example 3: Process a list in batches of size N

items=list(range(10))
batch_size=4

forstartinrange(0,len(items),batch_size):
batch=items[start:start+batch_size]
print(batch)

Example 4: Check two lists have the same length before zipping

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

iflen(names)!=len(scores):
raiseValueError("Lists must have the same length")

pairs=list(zip(names,scores))
print(pairs)

Example 5: Count items that match a condition

len() counts all items in a list, not items that match a rule. Filter first, then measure.

scores= [10,0,25,30]
non_zero_count=len([sforsinscoresifs!=0])

print(non_zero_count)

Common mistakes and how to fix them

Mistake 1: Off-by-one indexing

What you might do:

names= ["Amina","Luka","Noor"]
last=names[len(names)]

Why it breaks: Valid indexes stop at len(names) - 1, so len(names) is out of range.

Correct approach:

names= ["Amina","Luka","Noor"]
last=names[len(names)-1]

print(last)

Or use negative indexing:

names= ["Amina","Luka","Noor"]
last=names[-1]

print(last)

Mistake 2: Using length checks where you don’t need them

What you might do:

items= ["a","b","c"]

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

Why it breaks: Nothing crashes, but the code is harder to read and easier to mess up than a direct loop.

Correct approach:

items= ["a","b","c"]

foriteminitems:
print(item)

Mistake 3: Assuming len() tells you how many items match a rule

What you might do:

scores= [10,0,25,30]
count=len(scores!=0)

Why it breaks: scores != 0 does not filter the list and does not return something you can measure.

Correct approach:

scores= [10,0,25,30]
count=len([sforsinscoresifs!=0])

print(count)

Troubleshooting

If you see TypeError: object of type ... has no len(), the variable isn’t a list or another sized container. Print type(x) to confirm what you’re working with.

If you see IndexError: list index out of range, you likely used len(items) instead of len(items) - 1.

If your code returns an unexpected result for the last item, check for empty lists and watch out for -1 indexing.

If your loop feels complicated, try for item in items and avoid indexes unless you truly need them.

Quick recap

• Use len(my_list) to get the number of items.
• len([]) is 0, so empty lists are safe to measure.
• Valid indexes stop at len(my_list) - 1.
• Use if my_list: to check for emptiness.
• Filter first if you want the count of items that match a condition.