Python - Array Methods

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The following are the built-in methods of Python array module -

• reverse()
• count()
• index()
• fromlist()
• tofile()
• fromfile()

Python array.reverse() Method

Like the sequence types, the array class also supports the reverse() method which rearranges the elements in reverse order.

Syntax

array.reverse()

Parameters

This method has no parameters

Example

import array as arr
a = arr.array('i', [1, 2, 3, 4, 5])
a.reverse()
print (a)

It will produce the following output −

array('i', [5, 4, 3, 2, 1])

The array class also defines the following useful methods.

Python array.count() Method

The count() method returns the number of times a given element occurs in the array.

Syntax

array.count(v)

Parameters

• v − The value whose occurrences are to be counted

Return value

The count() method returns an integer corresponding the number of times v appears in the array.

Example

import array as arr
a = arr.array('i', [1, 2, 3, 2, 5, 6, 2, 9])
c = a.count(2)
print ("Count of 2:", c)

It will produce the following output −

Count of 2: 3

Python array.index() method

The index() method in array class finds the position of first occurrence of a given element in the array.

Syntax

array.index(v)

Parameters

• v − the value for which the index is to be found

Example

a = arr.array('i', [1, 2, 3, 2, 5, 6, 2, 9])
c = a.index(2)
print ("index of 2:", c)

It will produce the following output −

index of 2: 1

Python array.fromlist() Method

The fromlist() method appends items from a Python list to the array object.

Syntax

array.fromlist(l)

Parameters

• i − The list, items of which are appended to the array. All items in the list must be of same arrtype.

Example

import array as arr
a = arr.array('i', [1, 2, 3, 4, 5])
lst = [6, 7, 8, 9, 10]
c = a.fromlist(lst)
print (a)

It will produce the following output −

array('i', [1, 2, 3, 4, 5, 6, 7, 8, 9, 10])

Python array.tofile() Method

The tofile() method in array class writes all items (as machine values) in the array to the file object f.

Syntax

array.tofile(f)

Parameters

• f − the file object obtained with open() function. The file to be opened in wb mode.

Example

import array as arr
f = open('list.txt','wb')
arr.array("i", [10, 20, 30, 40, 50]).tofile(f)
f.close()

Output

After running the above code, a file named as "list.txt" will be created in the current directory.

Python array.fromfile() Method

The fromfile() method reads a binary file and appends specified number of items to the array object.

Syntax

array.fromfile(f, n)

Parameters

• f − The file object referring to a disk file opened in rb mode

• n − number of items to be appended

Example

import array as arr
a = arr.array('i', [1, 2, 3, 4, 5])
f = open("list.txt", "rb")
a.fromfile(f, 5)
print (a)

It will produce the following output −

array('i', [1, 2, 3, 4, 5, 10, 20, 30, 40, 50])