Array in Python | Set 1 (Introduction and Functions)

Other than some generic containers like lists, Python in its definition can also handle containers with specified data types. The array can be handled in Python by a module named “array“. They can be useful when we have to manipulate only specific data type values.

Properties of Arrays

• Each array element is of the same data type and size. For example: For an array of integers with the int data type, each element of the array will occupy 4 bytes.
• Elements of the array are stored in contiguous memory locations.

Operations on Array in Python

Below are some operations that can be performed in an array:

• append()
• insert()
• pop()
• remove()
• index()
• reverse()

array(data type, value list) in Python

This function is used to create an array with data type and value list specified in its arguments. Some data types are mentioned in the table below.

Type Code	C Type	Python Type	Minimum size in Bytes
‘b’	signed char	int	1
‘B’	unsigned char	int	1
‘u’	Py_UNICODE	Unicode character	2
‘h’	signed short	int	2
‘H’	unsigned short	int	2
‘i’	signed int	int	2
‘I’	unsigned int	int	2
‘l’	signed long	int	4
‘L’	unsigned long	int	4
‘q’	signed long long	int	8
‘Q’	unsigned long long	int	8
‘f’	float	float	4
‘d’	double	float	8

Python append() Method

This function is used to add the value mentioned in its arguments at the end of the array. In this example, we are adding an element at the end of the array.

Python3

# importing "array" for array operations
import array

# initializing array with array values and signed integers
arr = array.array('i', [1, 2, 3])

# printing original array
print ("The new created array is : ",end=" ")
for i in range (0, 3):
    print (arr[i], end=" ")
print("\r")

# using append() to insert new value at end
arr.append(4);

# printing appended array
print("The appended array is : ", end="")
for i in range (len(arr)):
    print (arr[i], end=" ")

Output

The new created array is :  1 2 3 
The appended array is : 1 2 3 4 

Array insert(i,x) Method in Python

This function is used to add the value(x) at the ith position specified in its argument. In this example, we are inserting an element at a specified index in an array.

Python3

# importing "array" for array operations
import array

# initializing array with array values and signed integers
arr = array.array('i', [1, 2, 3])

# printing original array
print ("The new created array is : ",end=" ")
for i in range (0, 3):
    print (arr[i], end=" ")

arr.insert(2, 5)

print("\r")

# printing array after insertion
print ("The array after insertion is : ", end="")
for i in range (len(arr)):
    print (arr[i], end=" ")

Output

The new created array is :  1 2 3 
The array after insertion is : 1 2 5 3 

Time Complexity: The initialization of the array takes O(n) time, where n is the number of elements in the array. The for loops used for printing the original array and the appended/inserted array takes O(n) time each, where n is the number of elements in the array. The append() method takes O(1) time as it adds the new element at the end of the array in constant time. The insert() method takes O(n) time in the worst case as it may have to shift all the elements to the right of the given position by one index, where n is the number of elements in the array. Therefore, the overall time complexity of the code is O(n) + O(n) + O(1) + O(n) = O(n).

Auxiliary Space: The array data structure used for initialization, append() and insert() methods requires a fixed amount of space for each element in the array. The space used by the print statements is negligible compared to the space used by the array. Therefore, the auxiliary space complexity of the code is O(n), where n is the number of elements in the array.

array pop() Method in Python

This function removes the element at the position mentioned in its argument and returns it. In this example, we are removing an element mentioned at a particular index.

Python3

# importing "array" for array operations
import array

# initializing array with array values
arr= array.array('i',[1, 2, 3, 1, 5])

# printing original array
print ("The new created array is : ",end="")
for i in range (0,5):
    print (arr[i],end=" ")

print("\r")

# using pop() to remove element at 2nd position
print ("The popped element is : ",end="")
print (arr.pop(2));

# printing array after popping
print ("The array after popping is : ",end="")
for i in range (len(arr)):
    print (arr[i],end=" ")

Output

The new created array is : 1 2 3 1 5 
The popped element is : 3
The array after popping is : 1 2 1 5 

Array remove() in Python

This function is used to remove the first occurrence of the value mentioned in its arguments. In this example, we are removing the first occurrence of 1 from a given array.

Python3

# importing "array" for array operations
import array

# initializing array with array values
arr= array.array('i',[1, 2, 3, 1, 5])

# printing original array
print ("The new created array is : ",end="")
for i in range (0,5):
    print (arr[i],end=" ")

print("\r")

# using remove() to remove 1st occurrence of 1
arr.remove(1)

# printing array after removing
print ("The array after removing is : ",end="")
for i in range (len(arr)):
    print (arr[i],end=" ")

Output

The new created array is : 1 2 3 1 5 
The array after removing is : 2 3 1 5 

Array index() Method

This function returns the index of the first occurrence of the value mentioned in the arguments. In this example, we are finding the index of 1st occurrence of 2 and printing it.

Python3

# importing "array" for array operations
import array

# initializing array with array values
arr= array.array('i',[1, 2, 3, 1, 2, 5])

# printing original array
print ("The new created array is : ",end="")
for i in range (0,6):
    print (arr[i],end=" ")

print("\r")

# using index() to print index of 1st occurrence of 2
print ("The index of 1st occurrence of 2 is : ",end="")
print (arr.index(2))

Output

The new created array is : 1 2 3 1 2 5 
The index of 1st occurrence of 2 is : 1

Array reverse() Function

This function reverses the array. In this example, we are reversing the array by using reverse().

Python3

# importing "array" for array operations
import array

# initializing array with array values
arr= array.array('i',[1, 2, 3, 1, 2, 5])

# printing original array
print ("The new created array is : ",end="")
for i in range (0,6):
    print (arr[i],end=" ")

print("\r")

#using reverse() to reverse the array
arr.reverse()

# printing array after reversing
print ("The array after reversing is : ",end="")
for i in range(len(arr)):
    print (arr[i],end=" ")

Output

The new created array is : 1 2 3 1 2 5 
The array after reversing is : 5 2 1 3 2 1 

Where can arrays be used?

• Arrays should be used where the number of elements to be stored is already known. 
• Arrays are commonly used in computer programs to organize data so that a related set of values can be easily sorted or searched. 
• Generally, when we require very fast access times, we usually prefer arrays since they provide O(1) access times. 
• Arrays work well when we have to organize data in multidimensional format. We can declare arrays of as many dimensions as we want. 
• If the index of the element to be modified is known beforehand, it can be efficiently modified using arrays due to quick access time and mutability.