Python List
List is collection of different objects which are
ordered and it is mutable. Since the declaration of all values follows the same
syntax “var = value”, based on the value representation the type of the var is
determined like other variable declaration.
Creation of List data:
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To create a list data type we can just give an empty square braces to a var
>>> Var = [] # creates an empty list objects and referred to Var.
>>> Var = list() # this also creates the same empty list
>>> Var = [1,2,'apple','baby'] #To create a list with static values, we have to give comma separated objects within square braces.
The same way we can pass an iterable to list function call
>>> Var = list("iterable") # -> [‘i’,’t’,’e’,’r’,’a’,’b’,’l’,’e’].
Adding elements into a list object:
To add the element to an existing object, we have two methods to perform adding the elements to a list:
Append -> used to add the object to the last index of the list object
obj.append(value)
Insert-> used to add the object at the specific index of the list object
obj.insert(index, value)
Example:
>>> a=['apple','banana']
>>> a.append('strawberry')
>>> a.append('mango')
>>> print(a)
['apple', 'banana', 'strawberry', 'mango']
>>> a.insert(1,'blueberry')
>>> print(a)
['apple', 'blueberry', 'banana', 'strawberry', 'mango']
>>>>>> a.insert(100,'cranberry')
>>> print(a)
['apple', 'blueberry', 'banana', 'strawberry', 'mango', 'cranberry']
>>>
Accessing
any values from list object:
Through indexing we can access any object from the list. For
example,
Syntax->
obj[index]
In Python, we can do both forward and reverse indexing. Forward
indexing starts from 0 to len(obj)-1.
Reverse indexing starts from -1 to last index.
>>> print(a) ['apple', 'blueberry', 'banana', 'strawberry', 'mango', 'cranberry'] >>> print(a[0]) apple >>> print(a[1]) blueberry >>> print(a[-1]) cranberry >>> print(a[-3]) strawberry >>> >>> for i in a: ... print(i, end =' ') ... apple blueberry banana strawberry mango cranberry >>>
Modify a
value from a list:
To modify a value from a list, we need to refer an index value and
assign a new value to it.
Syntax -> obj[index] = new_value
>>> print(a) ['apple', 'blueberry', 'banana', 'strawberry', 'mango', 'cranberry'] >>> a[2] = 'fruits' >>> print(a) ['apple', 'blueberry', 'fruits', 'strawberry', 'mango', 'cranberry'] >>>
Remove elements from a List:
There are three ways to delete any element from the list. They are:
>>> print(a)
['apple', 'blueberry', 'fruits', 'strawberry', 'mango', 'cranberry']
>>> del a[2]
>>> print(a)
['apple', 'blueberry', 'strawberry', 'mango', 'cranberry']
>>> a.pop()
'cranberry'
>>> print(a)
['apple', 'blueberry', 'strawberry', 'mango']
>>> a.pop(2)
'strawberry'
>>>
>>> print(a)
['apple', 'blueberry', 'mango']
>>> a.remove('apple')
>>> print(a)
['blueberry', 'mango']
>>> a.clear() #used to delete all the values in list and makes it empty
>>> a
[]
>>>
Merge two
list into one:
To merge two list into one we can use built-in extend method in list objects.
Syntax -> obj.extend(another_list)
>>> x=[1,2,3,4] >>> x [1, 2, 3, 4] >>> y=[6,8,9] >>> y [6, 8, 9] >>> x.extend(y) >>> x [1, 2, 3, 4, 6, 8, 9] >>>
