Dictionary in python

-
*Dictionary in python*

Dictionary

A dictionary is a collection which is unordered, changeable and indexed. In Python dictionaries are written with curly brackets, and they have keys and values.

Example

Create and print a dictionary:
thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
print(thisdic)

OUTPUT:-
{ "brand": "Ford","model": "Mustang","year": 1964} 

Accessing Items

You can access the items of a dictionary by referring to its key name, inside square brackets:

Example

Get the value of the "model" key:
x = thisdict["model"]
print(x)

OUTPUT:-
"Mustang"


OR

There is also a method called get() that will give you the same result:

Example

Get the value of the "model" key:
x = thisdict.get("model")print(x) 


OUTPUT:-
"Mustang"


Change Values

You can change the value of a specific item by referring to its key name:

Example

Change the "year" to 2018:
thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
thisdict["year"] = 2018
print(thisdict)  

OUTPUT:-

{"brand": "Ford","model": "Mustang","year": 2018}

Loop Through a Dictionary

You can loop through a dictionary by using a for loop.
When looping through a dictionary, the return value are the keys of the dictionary, but there are methods to return the values as well.

Example

Print all key names in the dictionary, one by one:
thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
for x in thisdict:
  print(x) 
OUTPUT:-
"brand"
 "model"
 "year"

or

Example

Print all values in the dictionary, one by one:
thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
for x in thisdict:
  print(thisdict[x]) 
OUTPUT:-
"Ford"
"Mustang"
1964
OR
  
Example
You can also use the values() function to return values of a dictionary:
thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
for x in thisdict.values():
  print(x) 
OUTPUT:-
 "Ford"
 "Mustang"
 1964
OR

Example

Loop through both keys and values, by using the items() function:
thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
for x, y in thisdict.items():
  print(x,":", y) 
OUTPUT:-
 
"brand": "Ford"
"model": "Mustang"
"year": 1964

Check if Key Exists

To determine if a specified key is present in a dictionary use the in keyword:

Example

Check if "model" is present in the dictionary:
thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
if "model" in thisdict:
  print("Yes, 'model' is one of the keys in the thisdict dictionary")


OUTPUT:-
"Yes, 'model' is one of the keys in the thisdict dictionary"

Dictionary Length

To determine how many items (key-value pairs) a dictionary has, use the len() method.

Example

Print the number of items in the dictionary:
thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
print(len(thisdict))

OUTPUT:-

3

Adding Items

Adding an item to the dictionary is done by using a new index key and assigning a value to it:

Example

thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
thisdict["color"] = "red"
print(thisdict)

OUTPUT:-
{"brand": "Ford","model": "Mustang","year": 1964,"color": "red"}

Removing Items

There are several methods to remove items from a dictionary:

Example

The pop() method removes the item with the specified key name:
thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
thisdict.pop("model")
print(thisdict) 
OUTPUT:-
{"brand": "Ford","year": 1964}
OR

Example

The popitem() method removes the last inserted item (in versions before 3.7, a random item is removed instead):
thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
thisdict.popitem()
print(thisdict) 
OUTPUT:-
{'brand': 'Ford', 'model': 'Mustang'} 
OR

Example

The del keyword removes the item with the specified key name:
thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
del thisdict["year"]
print(thisdict) 
OUTPUT:-
{'brand': 'Ford', 'model': 'Mustang'}
OR

Example

The del keyword can also delete the dictionary completely:
thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
del thisdict
print(thisdict)
OUTPUT:-
#this will cause an error because "thisdict" no longer exists.

Example

The clear() keyword empties the dictionary:
thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
thisdict.clear()
print(thisdict) 
OUTPUT
{}

Copy a Dictionary

You cannot copy a dictionary simply by typing dict2 = dict1, because: dict2 will only be a reference to dict1, and changes made in dict1 will automatically also be made in dict2.
There are ways to make a copy, one way is to use the built-in Dictionary method copy().

Example

Make a copy of a dictionary with the copy() method:
thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
mydict = thisdict.copy()
print(mydict)
OUTPUT:
{"brand": "Ford","model": "Mustang","year": 1964}
OR
Another way to make a copy is to use the built-in method dict().

Example

Make a copy of a dictionary with the dict() method:
thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
mydict = dict(thisdict)
print(mydict)
OUTPUT:
{"brand": "Ford","model": "Mustang","year": 1964}

The dict() Constructor

It is also possible to use the dict() constructor to make a new dictionary:

Example

thisdict = dict(brand="Ford", model="Mustang", year=1964)
# note that keywords are not string literals # note the use of equals rather than colon for the assignment print(thisdict)
OUTPUT:
{"brand": "Ford","model": "Mustang","year": 1964}

Dictionary Methods

Python has a set of built-in methods that you can use on dictionaries.
Method Description
clear()Removes all the elements from the dictionary
copy()Returns a copy of the dictionary
fromkeys()Returns a dictionary with the specified keys and values
get()Returns the value of the specified key
items()Returns a list containing the a tuple for each key value pair
keys()Returns a list containing the dictionary's keys
pop()Removes the element with the specified key
popitem()Removes the last inserted key-value pair
setdefault()Returns the value of the specified key. If the key does not exist: insert the key, with the specified value
update()Updates the dictionary with the specified key-value pairs
values()Returns a list of all the values in the dictionary
####################################################################################
 Thank you for visiting
do love and share and comment your questions i will definitelygive answer 

Test Yourself With Exercises

Exercise:

Use the get method to print the value of the "model" key of the car dictionary.
car ={
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
print()
 
what is the way to get the value ?? write in the comments in next blog 
i will give them shoutout 
 
 
and here is suggestion for you 

                                                                      


***
 

Comments

Post a Comment

Popular posts from this blog

Python Class and Objects

-
Image
Python Class and Objects What is class and object ? class :- it is a structure which is used to where you put your data and any function that you want  for example : if you buy any house it is full empty in that room you see a kitchen, bedroom, hall this we example of class and when you put something in the house like T.V, A.C, Sofa more.. it means you put some value on the class . in above left image is a class with no value and in right their is a class with value  for understanding replace class with hall and value with (TV, Sofa etc..) How we can implement class and object in python ? To create a class, use the keyword  class : Example : class   Room :         total_sofa =  5 this way we create class in python. How we can access class variable (ex: total_sofa ) value ? Answer: by using "object" let me explain don't get confuse  To create a object, we use : syntax : object = class_name() Create an object named p1, and print the value of total_sofa: Example : p1 = Room
Read more

Fibonacci series in python

-
Image
Fibonacci Series Fibonacci series is 0,1,1,2,3,5,8,13,21,34,............,infinity . It is a sequence of number which follow some type of algorithm the alogrithm is  let  i = index position  a = it is a array of number  so to find a[i+1] = a[i]+a[i-1]. Note : fibonacci series always start with 0 and 1 and goes upto infinity.you can't start with your own values. Explanation: 1. 0 and 1 in starting is default values  2. if we go further the algorithm start adding previous 2 value and the answer is the next value.     as you can see the previous two value is 0 and 1 after adding both we get 1 as our 3rd value.     after that adding 1 and 1 we get our 4th value as 2 this entire cycle goes like this only. i think you get better understanding about fibonacci series we move further on coding of fibo  in python: Flowchart: coding: without recursion function: def fibonacci(n):      a = 0      b = 1      if n < = 0 :          print ( "Incorrect input" )      else :          
Read more

exception handling in python

-
Image
EXCEPTION HANDLING IN PYTHON A Python program terminates as soon as it encounters an error. In Python, an error can be a syntax error or an exception. In this article, you will see what an exception is and how it differs from a syntax error. After that, you will learn about raising exceptions and making assertions. Then, you’ll finish with a demonstration of the try and except block. Exceptions versus Syntax Errors Syntax errors occur when the parser detects an incorrect statement. Observe the following example: >>> print ( 0 / 0 )) File " <stdin> " , line 1 print ( 0 / 0 )) ^ SyntaxError : invalid syntax     The arrow indicates where the parser ran into the syntax error . In this example, there was one bracket too many. Remove it and run your code again: >>> print ( 0 / 0 ) Traceback (most recent call last): File " <stdin> " , line 1 , in <module> ZeroDivisionError : int
Read more