Linux

How to Add an Item to List Using Append() Command

We have a list of numbers or strings, and we want to append items to a list. Basically, we can use the append method to achieve what we want.

The append() method adds a single item to the existing list. It doesn’t return a new list; rather it modifies the original list.

The syntax of append() method

list.append(item)

append() Parameters

The append() method takes a single item and adds it to the end of the list. The item can be numbers, strings, another list, dictionary etc.

1)  Adding Element to a List

Let’s look adding element to a list with an example

  # fruit list
  fruit = ['orange', 'apple', 'banana']

  # an element is added
  fruit.append('pineapple')

  #Updated Fruit List
  print('Updated fruit list: ', fruit)
  output
  Updated animal list: ['orange', 'apple', 'banana', 'pineapple']

as you see , 'pineapple' element has been added as last element.

2) Adding list to a list

Let’s see how to add list to a list

  # fruit list
  fruit = ['orange', 'apple', 'banana']

  # another list of green fruit
  green_fruit = ['green apple', 'watermelon']

  # adding green_fruit list to fruit list
  animal.append(green_fruit)

  #Updated List
  print('Updated animal list: ', fruit)
  output
  Updated animal list: ['orange', 'apple', 'banana', ['green apple', 'watermelon']]

As you see when append green_fruit list to fruit list, it goes as a list not two element.

3) Adding element of list to a list

Here we wil use extend() method to add element of list to another list, we will use the same pravious example to see the difference.

  # fruit list
  fruit = ['orange', 'apple', 'banana']

  # another list of green fruit
  green_fruit = ['green apple', 'watermelon']

  # adding green_fruit list to fruit list
  animal.extend(green_fruit)

  #Updated List
  print('Updated animal list: ', fruit)
  output
  Updated animal list: ['orange', 'apple', 'banana', 'green apple', 'watermelon']

As we saw, the green_fruit list has been added as elements not as a list to fruit list.

4) Adding element to a list with for loop

We will use For loop to append groups of element to list.

  # numbers list
  numbers = []

  # use for loop to fill numbers list with elements
  for i in range(10):
    numbers.append(i)

  #Updated List
  print('Updated numbers list: ', numbers)
  output
  Updated numbers list:  [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

We made empty list numbers and used for loop to append numbers in range from 0 to 9, so for loop in frist working append 0 and check number 2 in range or not, if in range append it and so on until reaching number 9, which add it and for loop stop working.

5) Adding element to a list with while loop

We will use While loop to append groups of element to list.

  # temperature list
  temperature = []

  # use while loop to fill temperature list with temperature degrees
  degree_value = 20
  degree_max = 50
  while degree_value <= degree_max:
      temperature.append(degree_value)
      degree_value += 5

  #Updated Temperature List
  print('Updated temperature list: ', temperature)
  output
  Updated temperature list:  [20, 25, 30, 35, 40, 45, 50]

we made empty list temperature and put start point degree_value and limit point degree_max and said, while degree_value less than or equal degree_max, append this value to temperature list, after that increase the value of degree_value five degrees, while loop will work until degree_value equal degree_max and stop working.

6) Appending two array using numpy module

We will use append method in numpy module to append two arrays.

  # import numpy module
  import numpy as np

  A = np.array([3])
  B = np.array([1,5,5])
  C = np.append(A, B)

  #print array C
  print('Array C: ', C)
  output
  Array C:  [3 1 5 5]

Note: you should install numpy module first by this command $ pip3 install numpy.

Conclusion

In this article, we have learned how to add an item in a list using Python append() command. Please let me know if you have any questions.

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