Python Lists
Tags: python, webdev, django
Published: 2020-04-23 09:35:55

In Python, lists are defined as arrayable elements which contain heterogeneous data values. It can have any numbers of rows but a single column. These lists can be sorted, inter-changed or modified.

Explaination :

    numbers = [1,2,3,4]
    
    #visual representation
    [
       0 : 1, # these are values
       1 : 2,
       2 : 3,
       3 : 4,
    ];
    

Indexing starts from zero [0], variables of different types can be stored in lists.

To create a list enter values separated by comma's in a square bracket and assign that bracket to a variable.

#### Accessing Lists

#### Example

Accessing list values are very simple and straight-forward. We simply need to specify the index of the value which we wish to use.

    simple_list = ['Jake', 25, 'New Jersey', 95255.00]
    
    print(simple_list)
    
    #PYTHON OUTPUT
    ['Jake', 25, 'New Jersey', 95255.0]

We will use the above example in creating a meaningful sentence.

#### Example

    simple_list = ['Jake', 25, 'New Jersey', 95255.00]
    
    print('%s is %d years old. He stays in %s and makes $%0.2f yearly income as Python Developer '%(simple_list[0], simple_list[1],simple_list[2], simple_list[3]))
    
    #PYTHON OUTPUT
    Jake is 25 years old. He stays in New Jersey and makes

> Note :  
> %s for strings variables  
> %d for interger variables  
> %f for float variables  
> They are called format specifiers.  
>   
> In `%0.2f` the letter `f` specifies float variable and `0.2` is the specifies the decimal point to be allowed.

#### Example

    x= 25.123456
    print('%0.1f'%(x))
    print('%0.2f'%(x))
    print('%0.3f'%(x))
    print('%0.4f'%(x))
    print('%0.5f'%(x))
    print('%0.6f'%(x))
    
    #PYTHON OUTPUT
    25.1
    25.12
    25.123
    25.1235
    25.12346
    25.123456

To update the value of a list. Assign list index in a square bracket to whichever value you would like to assign

#### Example

    simple_list = ['Jake', 25, 'New Jersey', 95255.00]
    
    simple_list[0] = 'Rohit' #updating value
    
    print(simple_list)
    
    #PYTHON OUTPUT
    ['Rohit', 25, 'New Jersey', 95255.0]

Appending new value into the list using `append()` method

Syntax

    list.append(value)

#### Example

    simple_list = ['Jake', 25, 'New Jersey', 95255.00]
    simple_list.append('New value added')
    print(simple_list)
    
    #PYTHON OUTPUT
    ['Jake', 25, 'New Jersey', 95255.0, 'New value added']

To remove a particular element from list use `remove()` method.

Syntax

    list.remove(value)

#### Example

    simple_list = ['Jake', 25, 'New Jersey', 95255.00]
    simple_list.remove('New Jersey') 
    print(simple_list)
    
    #PYTHON OUTPUT
    ['Jake', 25, 95255.0]

To empty values inside list use `clear()` method

Syntax

    list.clear(value)

#### Example

    simple_list = ['Jake', 25, 'New Jersey', 95255.00]
    simple_list.clear() 
    print(simple_list)
    
    #PYTHON OUTPUT
    []

To delete the list use `del` keyword before list variable

Syntax

    del list

#### Example

    simple_list = ['Jake', 25, 'New Jersey', 95255.00]
    del simple_list 
    print(simple_list)
    
    #PYTHON ERROR OUTPUT
    Traceback (most recent call last):
        print(simple_list)
    NameError: name 'simple_list' is not define

#### Iterating through lists

We will be using python's built-in `for-in` loop to display list data

    marks = [25,29,19,20]
    
    for i in marks:
        print(i)
    
    #PYTHON OUTPUT
    25
    29
    19
    20

Counting the numbers of elements present in list use `len()` method.

Syntax :

    len(list)

#### Example

    marks = [25,29,19,20]
    print(len(marks))
    
    #PYTHON OUTPUT
    4

To reverse a given elements in list use `list.reverse()` method.

Syntax :

    list.reverse()

#### Example

    marks = [25,29,19,20]
    marks.reverse()
    print(marks)
    
    #PYTHON OUTPUT
    [20, 19, 29, 25]

Check if the value exists in the list.

    marks = [25,29,19,20]
    
    if 25 in marks:
        print("Yes exists")
    else:
        print("Does not exists")
    
    #PYTHON OUTPUT
    Yes exists

The above example simply returns `True or False`

Click to check out the complete article on [python list](http://thecodelearners.com/python-lists/)