Python len() Function: Usage and Examples

A form limits the number of selected products.

What You Need to Understand

len(value) reports the number of elements in a supported collection, such as a list, tuple, dictionary or string. String length counts Unicode code points rather than UTF-8 bytes or user-visible grapheme clusters.

When to Use It

A form limits the number of selected products.

Step-by-Step Python Example

items = ["apple", "pear", "apple"]
print(len(items))
print(len("café"))
print(len({"one": 1, "two": 2}))

How the Example Works

The list contains three elements including the duplicate; the string has four Unicode code points; the dictionary has two keys.

Example Output

3
4
2
Empty

A Second Example

Compare this smaller variation with the main example, then experiment with your own values.

names = []
print(names[-1] if len(names) > 0 else "Empty")

Important Behavior and Edge Cases

len() does not count the contents of a generator without consuming it by another method. It raises TypeError on types that have no defined length.

Try It Yourself

Check the number of items before reading the last one.

Common Beginner Mistakes

len() does not count the contents of a generator without consuming it by another method. It raises TypeError on types that have no defined length.
Overlooking how an iterable is consumed, how element positions are chosen, or whether a function creates a new list.

Key Takeaways

len(value) reports the number of elements in a supported collection, such as a list, tuple, dictionary or string.
The list contains three elements including the duplicate; the string has four Unicode code points; the dictionary has two keys.
len() does not count the contents of a generator without consuming it by another method.