Python Lists

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.

Explanation :

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