Lists in python : []

Lists are a collection of data values stored as a list and values are separated by a comma.

To declare a list, you code as following :

We use square brackets [ ] when declaring a list.

list_name = [Multiple values are separated by a comma]

Example:

user_cars_colors = [‘red’, ‘yellow’, ‘black’, ‘blue’]

List commands in python

user_cars_colors = [‘red’, ‘yellow’, ‘black’, ‘blue’]

To assign user_cars_colors (from index 1 to 3) and print

user_cars_colors = user_cars_colors[1:3]

print (user_cars_colors)

>>>You’ll get [yellow, black]

In order to modify the second item in List and print the updated list

user_cars_colors[1] = ‘green’

print(user_cars_colors)

>>> [‘red’, ‘green’, ‘black’, ‘blue’]

To append a new item to user_cars_colors and print the list :

user_cars_colors.append(“white”)

print(user_cars_colors)

>>>[‘red’, ‘green’, ‘black’, ‘blue’, ‘white’]

To remove the fifth item from user_cars_colors and print the list :

del user_cars_colors [4]

print(user_cars_colors)

>>>[‘red’, ‘green’, ‘black’, ‘blue’]

len(): returns how many elements are in a list.

Users_cars_speeds = [100, 50, 30, 20,120]

len(Users_cars_speeds)

>>> 5

max() returns the greatest element of the list.

Users_cars_speeds = [100, 50, 30, 20,120]

max(Users_cars_speeds)

>>> 120

min(): returns the smallest element in a list.

Users_cars_speeds = [100, 50, 30, 20,120]

min(Users_cars_speeds)

>>> 20

sorted() returns a copy of a list ordered from smallest to largest

Users_cars_speeds = [100, 50, 30, 20,120]

sorted(Users_cars_speeds)

>>> 120, 100, 50, 30, 20

Sum():

returns the sum of the elements in a list.

>>> Users_cars_speeds = [100, 50, 30, 20,120]

>>>sum(Users_cars_speeds)

320

pop():

removes the last element from a list and returns it.

>>> Users_cars_speeds = [100, 50, 30, 20,120]

>>> Users_cars_speeds.pop

120

Using range( ) in list:

>>> x = range(5)

>>> print(x)
[0,1,2,3,4]
Zero = x[0] equals 0, lists are 0-indexed
One = x[1]
Two = x[2]

Three = x[3]

Four = x[4] fifth element of the x list of range(5).
Four = x[-1] fifth element of the x list of range(5).
>>>

Tuples : ()

Tuples are just like lists, but we cannot modify their data values.

Example:

Year_monthes = (“January”, “February”, “March”, “April”, “May”, “June”, “July”, “August”, “September”, “October”, “November”, “December”)

In order to access specific values of a tuple use their indexes like what we do with a list.

so, year_monthes [0] = “January”, & year_monthes [-1] = “December”

Del() tuple function:

This function will delete the whole tuple

[Example]

year_monthes = (“January”, “February”, “March”, “April”, “May”, “June”, “July”, “August”, “September”, “October”, “November”, “December”)

del year_monthes

print (year_monthes)

=> NameError: name ' year_monthes ' is not defined

In use for tuples:

This function will check if an item is in a tuple

[Example]

year_monthes = (“January”, “February”, “March”, “April”, “May”, “June”, “July”, “August”, “September”, “October”, “November”, “December”)

‘1’ in year_monthes

=> False

‘January’ in year_monthes

=> True

len( ) tuple function:

This function will calculate number of items in tuple.

[Example]

year_monthes = (“January”, “February”, “March”, “April”, “May”, “June”, “July”, “August”, “September”, “October”, “November”, “December”)

print (len(year_monthes))

>>> 12

Addition of tuples:

year_monthes = (“January”, “February”, “March”, “April”, “May”, “June”, “July”, “August”, “September”, “October”, “November”, “December”)

print (year_monthes +(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12))

>>>(“January”, “February”, “March”, “April”, “May”, “June”, “July”, “August”, “September”, “October”, “November”, “December”, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)

multiplication of tuples:

year_monthes = (“January”, “February”, “March”, “April”, “May”, “June”, “July”, “August”, “September”, “October”, “November”, “December”)

print (year_monthes * 2)

>>>(“January”, “February”, “March”, “April”, “May”, “June”, “July”, “August”, “September”, “October”, “November”, “December”, “January”, “February”, “March”, “April”, “May”, “June”, “July”, “August”, “September”, “October”, “November”, “December”)

Dictionary : {}

Dictionary is group of pairs of data values each pair have two parts

Dictionary key and data value {key1:value1, key2:value 2, etc….}

Example:

>>> User_name_and_car_color = { “David”:”red”, “John”:”green”, ”Sara”: “yellow”}

In order to declare a dictionary we use dict() method

>>> User_name_and_car_color = dict(David = red, John = green, Sara = yellow)

{“David”:”red”, “John”:”green”, ”Sara”: “yellow”}

In order to add a new item and print the updated dictionary:

>>>user_name_and_car_color[“Kate”] = “black”

>>>print(user_name_and_car_color)

{“Kate”, “black”, “David”:”red”, “John”:”green”, ”Sara”: “yellow”}

In order to remove the item with key = “Kate” and print dictionary:

>>>del user_name_and_car_color [“Kate”]

>>>print(user_name_and_car_color)

{“David”:”red”, “John”:”green”, ”Sara”: “yellow”}

Example:

>>>Print(user_name_and_car_color)

{“David”:”red”, “John”:”green”, ”Sara”: “yellow”}

In order to print the item with key = “David” code as following:

>>>print(user_name_and_car_color[“David”]) red

In order to print the item with key =Sara code as following:

>>> print(user_name_and_car_color[“Sara”])

yellow

In order modify the item with key = John and print the dictionary

>>> user_name_and_car_color[“John”] = “white”

>>>print(user_name_and_car_color”David”)

red

Dictionary .get() :

returns a value for the given key If the key is not found, it’ll return the keyword None.

Example:

user_name_and_car_color = {“David”:”red”, “John”:”green”, ”Sara”: “yellow”}

print(user_name_and_car_color)

>>>{“David”:”red”, “John”:”green”, ”Sara”: “yellow”}

print(user_name_and_car_color. get(“John”))

>>>green

user_name_and_car_color = {“David”:”red”,“John”:”green”, ”Sara”: “yellow”}

>>>print(user_name_and_car_color)

{“David”:”red”, “John”:”green”, ”Sara”: “yellow”}

print(user_name_and_car_color. get(“kate”))

None

Dictionary .del( ):

It delete the whole dictionary.

Example:

>>> user_name_and_car_color = {“David”:”red”, “John”:”green”, ”Sara”: “yellow”}

>>> user_name_and_car_color.del()

>>>print (user_name_and_car_color)

NameError: name 'dic1' is not defined

Dictionary .clear( ):

It removes all elements of the dictionary, returning an empty dictionary

Example:

>>> user_name_and_car_color = {“David”:”red”, “John”:”green”, ”Sara”: “yellow”}

>>> user_name_and_car_color.clear()

>>>print (user_name_and_car_color)

{ }

Dictionary In( ):

We use it to check if an item is in a dictionary

Example:

>>>user_name_and_car_color = {“David”:”red”, “John”:”green”, ”Sara”: “yellow”}

Use it on the key

>>>David in user_name_and_car_color

True

>>>Kate in user_name_and_car_color

False

Use It on the value:

Example:

user_name_and_car_color = {“David”:”red”, “John”:”green”, ”Sara”: “yellow”}

‘red’ in user_name_and_car_colo.values()

=> True

‘black’ in user_name_and_car_colo.values()

=> False

Dictionary .items( )

We use it to return a list of dictionary’s pairs as tuples

[Example]

user_name_and_car_color = {“David”:”red”, “John”:”green”, ”Sara”: “yellow”}

user_name_and_car_color.items()

>>> dict_items([(“David”:”red”), (“John”:”green”), (”Sara”: “yellow”)])

Dictionary .len( ):

We use it to calculate the number of items in a dictionary

Example:

>>>year_monthes = {“January” : 1, “February” : 2, “March” : 3, “April”: 4, “May”: 5, “June”: 6, “July”: 7, “August”: 8, “September”: 9, “October”: 10, “November”: 11, “December”: 12 }

>>> print (len(year_monthes))

12

>>>

Dictionary . update( ):

We use this to Add one dictionary’s key-values pairs to another. Duplicates are removed.

Example:

>>> year_monthes = {“January” : 1, “February” : 2, “March” : 3, “April”: 4, “May”: 5, “June”: 6}

>>> second_six_year_monthes = {“July”: 7, “August”: 8, “September”: 9, “October”: 10, “November”: 11, “December”: 12}

>>> year_monthes.update(second_six_year_monthes)

>>> print (year_monthes)

{“January” : 1, “February” : 2, “March” : 3, “April”: 4, “May”: 5, “June”: 6, “July”: 7, “August”: 8, “September”: 9, “October”: 10, “November”: 11, “December”: 12 }

>>>print second_six_year_monthes

{“July”: 7, “August”: 8, “September”: 9, “October”: 10, “November”: 11, “December”: 12}

So there is no change in second_six_year_monthes dictionary.

Dictionary . values( )

This will returns list of the dictionary's values

Example:

>>> year_monthes = {“January” : 1, “February” : 2, “March” : 3, “April”: 4, “May”: 5, “June”: 6, “July”: 7, “August”: 8, “September”: 9, “October”: 10, “November”: 11, “December”: 12 }

>>>year_monthes.values()

dict_values([‘1', ‘2‘, ‘3', ‘4‘, ‘5', ‘6‘, ‘7', ‘8‘, ‘9', ‘10‘, ‘11', ‘12‘])

Dictionary . keys( )

We use it to returns list of the dictionary's keys

[Example]

>>> year_monthes = {“January” : 1, “February” : 2, “March” : 3, “April”: 4, “May”: 5, “June”: 6, “July”: 7, “August”: 8, “September”: 9, “October”: 10, “November”: 11, “December”: 12 }

>>> year_monthes.keys()

dict_keys([“January”, “February”, “March”, “April”, “May”, “June”, “July”, “August”, “September”, “October”, “November”, “December”])

Sets:

set is data structure, which represents a collection ofspecific elements:
set = set()
set.add(a)
set.add(b)
set.add(c)
x = len(set) print(x) >>>x= 3
y = d in set print(y) >>>y= False
z = c in set print(z) >>>z= False

Why it is preferred to use sets?

1. It is a very fast code operation on sets than lists.
2. set is it more appropriate than a list, If we have a large collection of items that we want to use for elements presence in set test:

>>> x = [1,2,3,4,5,6,7,8,9,10]

>>>print(1 in set(x), 15 in set(x),20 in set(x))

(True, False, False)