Python summary: methods for lists

We will view the functions which can be used for lists:

• list.append(item)
• list.extend(item)
• list.insert(index, item)
• list.remove(item)
• list.pop(index)
• list.clear()
• list.index(item)
• list.count(item)
• list.sort()
• list.reverse()
• list.copy()

Let’s start with:

>>> animals = ['cat', 'dog', 'bee']

And for each method we will imagine if we had done this:

>>> animals = ['cat', 'dog', 'bee'] # Creating the dictionary again

(#) To add one item to the end of list:

list.append(item)

>>> animals.append('eagle')
>>> ['cat', 'dog', 'bee', 'eagle']

>>> couple = ['cow', 'bull']
>>> animals.append(couple)
>>> animals
['cat', 'dog', 'bee', 'eagle', ['cow', 'bull']

(#) To concatenate an item to the end of list:

list.extend(item)

>>> animals.extend('eagle')
>>> ['cat', 'dog', 'bee', 'eagle']

>>> couple = ['cow', 'bull']
>>> animals.extend(couple)
>>> animals
['cat', 'dog', 'bee', 'eagle', 'cow', 'bull']

(#) To insert one item at a given position, moving to the right which had:

list.insert(index, item)

>>> animals.insert(2, 'eagle')
>>> animals
['cat', 'dog', 'eagle', 'bee']

(#) To delete an item, the first found with whose element:

list.remove(item)

>>> animals.append('dog')
>>> animals
['cat', 'dog', 'bee', 'dog']
>>> animals.remove('dog')
>>> animals
['cat', 'bee', 'dog']

(#) To remove and catch an item:

list.pop(index)

>>> animals
['cat', 'dog', 'bee']
>>> animals.pop(1)
'dog'
>>> animals
['cat', 'bee']

If no index is specified, the method catches the last item in the list:

>>> animals
['cat', 'dog', 'bee']
>>> animals.pop()
'bee'
>>> animals
['cat', 'dog']

(#) To remove all items:

list.clear()

>>> animals.clear()
'dog'
>>> animals
[]

(#) To return the first index of an item:

list.index(item)

>>> animals.append('dog')
>>> animals['cat', 'dog', 'bee', 'dog']
>>> animals.index('dog')
1

(#) To return the times which an item appears:

list.count('dog')

>>> animals.append('dog')
>>> animals['cat', 'dog', 'bee', 'dog']
>>> animals.index('dog')
2

(#) To sort the items (e.g., alphabetically):

list.sort()

>>> animals
['cat', 'dog', 'bee']
>>> animals.sort()
['bee', 'cat', 'dog']

(#) To do the opossite than sort():

list.reverse()

>>> animals
['cat', 'dog', 'bee']
>>> animals.reverse()
>>> animals
['bee', 'dog', 'cat']

(#) To copy a list as independent:

list.copy()

>>> myanimals = animals
>>> myanimals
['cat', 'dog', 'bee']
>>> animals.append('cow')
>>> myanimals
['cat', 'dog', 'bee', 'cow']
>>> myanimals is animals
True
>>> animals.copy()

The copy() method does not run to me, however it is possible to use the list() function for example (read below, on more information):

>>> animals = ['cat', 'dog', 'bee']
>>> myanimals = list(animals) # new_list = list(old_list)
>>> animals.append('cow')
>>> myanimals
['cat', 'dog', 'bee']
>>> myanimals is animals
False

More information:

• https://docs.python.org/3/tutorial/datastructures.html
• http://stackoverflow.com/questions/2612802/how-to-clone-or-copy-a-list-in-python
• https://docs.python.org/3.3/library/functions.html#func-list

Enric Baltasar

Reality builder, marketing passionate and entrepreneur.