Data Type - 'list' for Mutable List

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∟Data Type - 'list' for Mutable List

This section describes the 'list' data type, which stores a sequence of references to data objects of any data types. 'list' data objects are mutable.

What Is the "list" Data Type? "list" is the mutable list data type in Python. Each element in a "list" object stores a reference to another data object.

"list" data type has the following main Features.

1. "list" data objects can be created in several ways:

Using listed objects within brackets like ['apple', 'orange'], etc.
Using the cast function, list(object), like list(('apple', 'orange')), etc.

Here are some examples on how to create "tuple" objects:

>>> [9, 1, 1]
[9, 1, 1]

>>> ['nine', 'one', 'one']
['nine', 'one', 'one']

# elements are of different data types
>>> ['nine', b'one', 1]
['nine', b'one', 1]

>>> list((9, 1, 1))
[9, 1, 1]

# a "str" object is a sequence of multiple characters
>>> list('911')
['9', '1', '1']

# ('911') is a single "str" object
>>> list(('911'))
['9', '1', '1']

# ('911',) is a "tuple" object
>>> list(('911',))
['911']

2. "list" data type provides an array-style expression to access the element of a given position.

>>> x = ['nine', b'one', 1]
>>> type(x)
<class 'list'>

>>> e = x[0]
>>> e
'nine'
>>> type(e)
<class 'str'>

3. "list" data type is a mutable data type. Once a "list" data object is created to store a sequence of references, this sequence can be changed: elements can be added, removed and/or updated.

>>> x = ['nine', b'one', 1]
>>> id(x)
4459207552

>>> x.append('help')
>>> x
['nine', b'one', 1, 'help']

>>> x.remove(1)
>>> x
['nine', b'one', 'help']

>>> x[0] = 'ten'
>>> x
['ten', b'one', 'help']

>>> id(x)
4459207552

4. "list" objects support the following operations:

    Syntax   Operation       Note
----------   -------------   -----------------------
     x + y   Concatenation   Creates a new "list"
    x += y   Append          Updates x
     x * n   Repetition      n is an "int"
     n * x   Repetition      Same as x * n
    x *= n   Repetition      Updates x by repetition
    s in x   Look up         s is an object
s not in x   Look up         Same as !(s in x)
  x[i] = o   Update
  del x[i]   Delete

5. Some built-in functions are provided for "list" objects.

len(x) - Returns the number of elements in this "list" object.

6. Some instance methods are provided for "list" objects.

list.append(object) - Instance method appends the given object to the end of this list.
list.clear() - Instance method removes all elements from this list.
list.copy() - Instance method returns a new "list" object with same elements as in this list.
list.count(object) - Instance method returns the number of occurrences of the given object in this list.
list.extend(iterable) - Instance method extends this list with by extracting items from the given iterable.
list.find(object) - Instance method returns the lowest index in this list where the given object is found. Returns -1, if the given object is not found.
list.index(object) - Instance method returns the lowest index in this list where the given object is found. Raises ValueError, if the given object is not found.
list.insert(i, object) - Instance method inserts an extra element at the given index i.
list.pop(i) - Instance method pops out the element at the given index from this list. Pops out the last element, if i is not provided.
list.remove(object) - Instance method removes the given object from this list.
list.reverse() - Instance method reverses the order of elements in this list.
list.sort() - Instance method sorts elements in this list, if they are sortable.