The built-in Python function that returns an object's length is len.
Called as len(object), it reports the number of items in a sequence or collection. It works with familiar objects such as strings, lists, tuples, dictionaries, sets, and ranges: len("Python") returns 6, while len({"a": 1, "b": 2}) returns 2. For a dictionary, the count is of keys, not individual values.
Python makes len broadly useful through the __len__ special method. Custom classes can define __len__ so their instances respond to len(). The function asks the object for that size rather than requiring a separate length routine for every data type.
A common mix-up is assuming len() measures memory usage, character display width, or the number of bytes. It does none of those. For text, it counts Python string elements, while visual characters such as emoji sequences can involve multiple code points. len() also differs from count(), which searches for occurrences of a particular value.