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How to calculate the length of an array in Python?

An array is not a built-in data type in Python, but we can create arrays using third-party libraries. By length of an array, we mean the total number of elements or items in the given array. In order to calculate the length of an array, we can use various methods discussed below in this blog.

Table of contents

1. Length of array
2. Finding the length of an array using the len() function
3. Using Numpy to find the length of an array in Python
4. Closing thoughts

Length of array

In Python, an array is a collection of items stored at contiguous memory locations. It is a special variable, which can hold more than one value with the same data type at a time. We know array index starts from 0 instead of 1, therefore the length of an array is one more than the highest index value of the given array.

Finding the length of an array using the len() function

To find the length of an array in Python, we can use the len() function. It is a built-in Python method that takes an array as an argument and returns the number of elements in the array. The len() function returns the size of an array.

Syntax:

Input:

arr = [0, 1, 2, a, 4] print ("The given array is: ") print (arr) # Finding length of the given array size = len(arr) print ("The length of array is: ") print (size) 

Output:

The given array is: [0, 1, 2, a, 4] The length of array is: 5

Using Numpy to find the length of an array in Python

Another method to find the length of an array is Numpy «size». Numpy has a size attribute. The size is a built-in attribute that returns the size of the array.

Syntax:

Input:

import numpy as np arr = np.array([0, 1, 2, a, 4]) print ("The given array is: ") print (arr) # Finding length of the given array size = arr.size print ("The length of array is: ") print (size) 

Output:

The given array is: [0, 1, 2, a, 4] The length of array is: 5

Closing thoughts

Unlike other programming languages like JavaScript, PHP or C++, Python does not support «length()» or «size()» functions to find the length of an array. The len() function takes the array as a parameter and returns the size. One can read more about other Python concepts here.

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Length of Array in Python

We have learned that arrays are a collection of objects , and these collections can have any number of objects: zero, one, ten, and so on. The number of objects in the array is called its length. We need to know the length of an array to perform various operations like iterating over the array, checking whether an element belongs to the array and reading/updating elements in the array.

Introduction

Let us take an array as follows:

How many elements are in the array? The answer is 5. Hence the length of the array is also 5.

If we were to give indexes to each element in the array as follows:

Essentially, the length of an array is the highest index position + 1.

Array Length in Python using the len() method

Python has a len() method to find out the length of an array. The syntax is as follows:

Finding the Length of a Python NumPy Array

Numpy is a library compatible with Python for operating complex mathematical operations on multi-dimensional arrays . We use numpy for mathematical operations on arrays. Here is how we can find the length of an array in Python using numpy:

Conclusion

• Length of an array is the number of elements present in the array.
• In python, the length of an array is the highest index of an array + 1 .
• We can use Python’s len() function to find the length of an array.
• For a Numpy array also, we can use the len() function to find the array’s length in Python .

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array — Efficient arrays of numeric values¶

This module defines an object type which can compactly represent an array of basic values: characters, integers, floating point numbers. Arrays are sequence types and behave very much like lists, except that the type of objects stored in them is constrained. The type is specified at object creation time by using a type code, which is a single character. The following type codes are defined:

It can be 16 bits or 32 bits depending on the platform.

Changed in version 3.9: array(‘u’) now uses wchar_t as C type instead of deprecated Py_UNICODE . This change doesn’t affect its behavior because Py_UNICODE is alias of wchar_t since Python 3.3.

The actual representation of values is determined by the machine architecture (strictly speaking, by the C implementation). The actual size can be accessed through the array.itemsize attribute.

The module defines the following item:

A string with all available type codes.

The module defines the following type:

class array. array ( typecode [ , initializer ] ) ¶

A new array whose items are restricted by typecode, and initialized from the optional initializer value, which must be a list, a bytes-like object , or iterable over elements of the appropriate type.

If given a list or string, the initializer is passed to the new array’s fromlist() , frombytes() , or fromunicode() method (see below) to add initial items to the array. Otherwise, the iterable initializer is passed to the extend() method.

Array objects support the ordinary sequence operations of indexing, slicing, concatenation, and multiplication. When using slice assignment, the assigned value must be an array object with the same type code; in all other cases, TypeError is raised. Array objects also implement the buffer interface, and may be used wherever bytes-like objects are supported.

Raises an auditing event array.__new__ with arguments typecode , initializer .

The typecode character used to create the array.

The length in bytes of one array item in the internal representation.

Append a new item with value x to the end of the array.

Return a tuple (address, length) giving the current memory address and the length in elements of the buffer used to hold array’s contents. The size of the memory buffer in bytes can be computed as array.buffer_info()[1] * array.itemsize . This is occasionally useful when working with low-level (and inherently unsafe) I/O interfaces that require memory addresses, such as certain ioctl() operations. The returned numbers are valid as long as the array exists and no length-changing operations are applied to it.

When using array objects from code written in C or C++ (the only way to effectively make use of this information), it makes more sense to use the buffer interface supported by array objects. This method is maintained for backward compatibility and should be avoided in new code. The buffer interface is documented in Buffer Protocol .

“Byteswap” all items of the array. This is only supported for values which are 1, 2, 4, or 8 bytes in size; for other types of values, RuntimeError is raised. It is useful when reading data from a file written on a machine with a different byte order.

Return the number of occurrences of x in the array.

Append items from iterable to the end of the array. If iterable is another array, it must have exactly the same type code; if not, TypeError will be raised. If iterable is not an array, it must be iterable and its elements must be the right type to be appended to the array.

Appends items from the string, interpreting the string as an array of machine values (as if it had been read from a file using the fromfile() method).

New in version 3.2: fromstring() is renamed to frombytes() for clarity.

Read n items (as machine values) from the file object f and append them to the end of the array. If less than n items are available, EOFError is raised, but the items that were available are still inserted into the array.

Append items from the list. This is equivalent to for x in list: a.append(x) except that if there is a type error, the array is unchanged.

Extends this array with data from the given unicode string. The array must be a type ‘u’ array; otherwise a ValueError is raised. Use array.frombytes(unicodestring.encode(enc)) to append Unicode data to an array of some other type.

Return the smallest i such that i is the index of the first occurrence of x in the array. The optional arguments start and stop can be specified to search for x within a subsection of the array. Raise ValueError if x is not found.

Changed in version 3.10: Added optional start and stop parameters.

Insert a new item with value x in the array before position i. Negative values are treated as being relative to the end of the array.

Removes the item with the index i from the array and returns it. The optional argument defaults to -1 , so that by default the last item is removed and returned.

Remove the first occurrence of x from the array.

Reverse the order of the items in the array.

Convert the array to an array of machine values and return the bytes representation (the same sequence of bytes that would be written to a file by the tofile() method.)

New in version 3.2: tostring() is renamed to tobytes() for clarity.

Write all items (as machine values) to the file object f.

Convert the array to an ordinary list with the same items.

Convert the array to a unicode string. The array must be a type ‘u’ array; otherwise a ValueError is raised. Use array.tobytes().decode(enc) to obtain a unicode string from an array of some other type.

When an array object is printed or converted to a string, it is represented as array(typecode, initializer) . The initializer is omitted if the array is empty, otherwise it is a string if the typecode is ‘u’ , otherwise it is a list of numbers. The string is guaranteed to be able to be converted back to an array with the same type and value using eval() , so long as the array class has been imported using from array import array . Examples:

array('l') array('u', 'hello \u2641') array('l', [1, 2, 3, 4, 5]) array('d', [1.0, 2.0, 3.14]) 

Packing and unpacking of heterogeneous binary data.

Packing and unpacking of External Data Representation (XDR) data as used in some remote procedure call systems.

The NumPy package defines another array type.

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How to Find the Array Length in Python

Python len() method is used to find the length of an array. As we all know, python does not support or provide us with the array data structure in a direct way. Instead, python serves with three different variations of using an array data structure.

In this tutorial, we will learn about the fundamentals of the different array variants that can use to create an array in python and then we will discuss the use of the len() method to obtain the length of an array in each variant.

Finding the length of an Array using the len() Method

We have three methods to create an array in Python, which we will use to demonstrate the use of the len() method.

To demonstrate the len() method, we’ll use all of these types of arrays, but before that let’s take a look at the syntax of len() method.

len() Method in Python

Python len() method enables us to find the total number of elements in an array. It returns the count of the elements in an array.

Here, the array can be any type of array for which we want to find the length.

Finding the Length of a Python List using len() Method

The Python len() method can be used to fetch and display the number of elements contained in the list.

In the below example, we have created a list of heterogeneous elements. Further, we have used len() method to display the length of the list.

lst = [1,2,3,4,'Python'] print("List elements: ",lst) print("Length of the list:",len(lst))

List elements: [1, 2, 3, 4, 'Python'] Length of the list: 5

Finding the Length of a Python Array using len() Method

Python Array module helps us create an array and manipulate the same using various functions of the module. The len() method can also be used to calculate the length of an array created using the Array module.

import array as A arr = A.array('i',[1,2,3,4,5]) print("Array elements: ",arr) print("Length of array: ",len(arr))

Array elements: array('i', [1, 2, 3, 4, 5]) Length of array: 5

Finding the Length of a Python NumPy Array using len() Method

As we all know, we can create an array using NumPy module and use it for any mathematical purpose. The len() method helps us find out the number of data values present in a NumPy array.

import numpy as np arr = np.arange(5) len_arr = len(arr) print("Array elements: ",arr) print("Length of NumPy array: ",len_arr)

Array elements: [0 1 2 3 4] Length of NumPy array: 5

Conclusion

In this tutorial, we learned to use the len() method to find the length of different arrays in Python. We have given you many examples so that you can learn them well. Hope you find this tutorial useful.

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