5.10 Other List Methods

In [1]:
color_names = ['orange', 'yellow', 'green']

Inserting an Element at a Specific List Index

In [2]:
color_names.insert(0, 'red')
In [3]:
color_names
Out[3]:
['red', 'orange', 'yellow', 'green']

Adding an Element to the End of a List

In [4]:
color_names.append('blue')
In [5]:
color_names
Out[5]:
['red', 'orange', 'yellow', 'green', 'blue']

Adding All the Elements of a Sequence to the End of a List

  • Equivalent to +=.
In [6]:
color_names.extend(['indigo', 'violet'])
In [7]:
color_names
Out[7]:
['red', 'orange', 'yellow', 'green', 'blue', 'indigo', 'violet']
In [8]:
sample_list = []
In [9]:
s = 'abc'
In [10]:
sample_list.extend(s)
In [11]:
sample_list
Out[11]:
['a', 'b', 'c']
In [12]:
t = (1, 2, 3)
In [13]:
sample_list.extend(t)
In [14]:
sample_list
Out[14]:
['a', 'b', 'c', 1, 2, 3]
  • Parentheses are required for the tuple argument below, because extend expects one iterable argument.
In [15]:
sample_list.extend((4, 5, 6))  # note the extra parentheses
In [16]:
sample_list
Out[16]:
['a', 'b', 'c', 1, 2, 3, 4, 5, 6]

Removing the First Occurrence of an Element in a List

  • ValueError occurs if remove’s argument is not in the list.
In [17]:
color_names.remove('green')
In [18]:
color_names
Out[18]:
['red', 'orange', 'yellow', 'blue', 'indigo', 'violet']

Emptying a List

In [19]:
color_names.clear()
In [20]:
color_names
Out[20]:
[]

Counting the Number of Occurrences of an Item

In [21]:
responses = [1, 2, 5, 4, 3, 5, 2, 1, 3, 3, 
             1, 4, 3, 3, 3, 2, 3, 3, 2, 2]
In [22]:
for i in range(1, 6):
    print(f'{i} appears {responses.count(i)} times in responses')

1 appears 3 times in responses
2 appears 5 times in responses
3 appears 8 times in responses
4 appears 2 times in responses
5 appears 2 times in responses

Reversing a List’s Elements

  • Method reverse reverses the contents of a list in place.
In [23]:
color_names = ['red', 'orange', 'yellow', 'green', 'blue']
In [24]:
color_names.reverse()
In [25]:
color_names
Out[25]:
['blue', 'green', 'yellow', 'orange', 'red']

Copying a List

  • Method copy returns a new list containing a shallow copy.
In [26]:
copied_list = color_names.copy()
In [27]:
copied_list
Out[27]:
['blue', 'green', 'yellow', 'orange', 'red']

©1992–2020 by Pearson Education, Inc. All Rights Reserved. This content is based on Chapter 5 of the book Intro to Python for Computer Science and Data Science: Learning to Program with AI, Big Data and the Cloud.

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