How does len () work in python?
Watch Now This tutorial has a related video course created by the Real Python team. Watch it together with the written tutorial to deepen your understanding: Python's len() Function Show
In many situations, you’ll need to find the number of items stored in a data structure. Python’s built-in function There are
some cases in which the use of In this tutorial, you’ll learn how to:
By the end of this article, you’ll know when to use the Getting Started With Python’s len()The function You can start by looking at the help for this function: >>>
The function takes an object as an argument and returns the length of that object. The documentation for
When you use built-in data types and many third-party types with In the following sections, you’ll learn about how to use Using len() With Built-in SequencesA sequence is a container with ordered items. Lists, tuples, and strings are three of the basic built-in sequences in
Python. You can find the length of a sequence by calling >>>
When finding the length of the string The function >>>
In the examples above, you find the length of an empty string, an empty list, and an empty tuple. The function returns A >>>
This range of numbers includes the integers from In this section, you’ve used the Using len() With Built-in CollectionsAt some point, you may need to find the number of unique items in a list or another sequence. You can use sets and >>>
You generate the list Another built-in data type that you’ll use often is the dictionary. In a dictionary, each item consists of a key-value pair. When you use a dictionary as an argument for >>>
The output from the first example shows that there are three
key-value pairs in this dictionary. As was the case with sequences, Exploring len() With Other Built-in Data TypesYou
can’t use all built-in data types as arguments for >>>
The integer, float, Boolean, and
complex types are examples of built-in data types that you can’t use with You can also explore whether it’s possible to use iterators and generators as arguments for >>>
You’ve already seen that a list
has a length, meaning you can use it as an argument in You get a You can’t use generators with Exploring len() Further With Some ExamplesIn this section, you’ll learn about some common use cases for Verifying the Length of a User InputA common use case of
In this example, you use an
The username is nine characters long in this case, so the condition in the
In this case, Ending a Loop Based on the Length of an ObjectYou’ll use
You’re now using the result from You could even use >>>
You use the list method There’s a more Pythonic way of achieving the same output by using the truthiness of sequences: >>>
An empty list is falsy. This means that the Finding the Index of the Last Item of a SequenceImagine you want to generate a sequence of random numbers in the range >>>
You append random numbers to the list until the sum exceeds You want to remove the last number in the list so that the sum of all numbers in the list doesn’t exceed Splitting a List Into Two HalvesIf you need to split a sequence into two halves, you’ll need to use the index that represents the midpoint of the sequence. You can use >>>
In the assignment statement where you define
In the next assignment, where you define If your original list contains an odd number of items, then half of its length will no longer be a whole number. When you use integer division, you obtain the floor of the number. The list You can try this out by creating an initial list of eleven numbers instead of ten. The resulting lists will no longer be halves, but they’ll represent the closest alternative to splitting an odd sequence. Using the len() Function With Third-Party LibrariesYou
can also use Python’s NumPy’s ndarrayThe
NumPy module is the cornerstone of all quantitative applications of programming in Python. The module introduces the Before you can start using NumPy, you’ll
need to install the library. You can use Python’s standard package manager,
You’ve installed NumPy, and now you can create a NumPy array from a list and use >>>
The NumPy function
However, NumPy arrays can have more than one dimension. You can create a two-dimensional array by converting a list of lists into an array: >>>
The list To get the size of both dimensions, you use the property In general, when you have an array with any number of dimensions, >>>
In this example, you create a three-dimensional array with the shape Check out NumPy Tutorial: Your First Steps Into Data Science in Python to learn more about using NumPy arrays. Pandas’ DataFrameThe Before you can use pandas, you’ll need to install it by using the following command in the console:
You’ve installed the pandas package, and now you can create a DataFrame from a dictionary: >>>
The dictionary’s keys are strings representing the names of students in a class. The value of each key is a list with the marks for three subjects. When you create a DataFrame from this dictionary, you define the index using a list containing the subject names. The DataFrame has three rows and four columns. The function You’ve seen
how You can explore the pandas module further in The Pandas DataFrame: Make Working With Data Delightful. Using len() on User-Defined ClassesWhen you define a class, one of the special methods you can define is In the previous section, you’ve seen how
This method returns the length of the DataFrame’s You can explore the
The For this toy class, you define the object’s length as the number of occurrences of the letter Y in the string. Therefore, the You can create an object of class >>>
You create an object of type The Another special method is the >>>
The variable You can read more about using object-oriented programming and defining classes in Object-Oriented Programming (OOP) in Python 3. ConclusionYou’ve explored how to use The In this tutorial, you’ve learned how to:
You now have a good foundation for understanding the Watch Now This tutorial has a related video course created by the Real Python team. Watch it together with the written tutorial to deepen your understanding: Python's len() Function What does the LEN () list method do?Len() Method
There is a built-in function called len() for getting the total number of items in a list, tuple, arrays, dictionary, etc. The len() method takes an argument where you may provide a list and it returns the length of the given list.
How long does Len () in python take?The len() function in Python has a very peculiar characteristic that one had often wondered about. It takes absolutely no time, and equal time, in calculating the lengths of iterable data structures(string, array, tuple, etc.), irrespective of the size or type of data. This obviously implies O(1) time complexity.
What does Len 1 mean in python?len(A)-1 actually is the index of the last element in list A . As in python (and almost all programming languages), array indexes start from 0, so an array with n elements has index of 0, 1, 2, ..., n-1 . Follow this answer to receive notifications.
What is the output of Len ([ 1 2 3 ]) in python?What is the output of len([1, 2, 3])? Ans: 3.
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