Python Concepts For Data Science: Dictionaries

Python Dictionaries:

Python dictionary is an unordered collection of items. Each item of a dictionary has a key/value pair.

Each key is separated from its value by a colon (:), the items are separated by commas, and the whole thing is enclosed in curly braces. An empty dictionary without any items is written with just two curly braces, like this: {}.

dict ={

"Name": "Any_name",

"Age": "18",

}

This is how the python dictionary looks. Here 'name' and "age' are the keys while 'any_name' and '18' are their corresponding values in the dictionary named 'dict'.

Creating a dictionary:

In Python, a Dictionary can be created by placing a sequence of elements within curly {} braces, separated by ‘comma’. Dictionary holds a pair of values, one being the Key and the other corresponding pair element being its Key:value.

dict ={
 
 "Name": "Any_name" ,
 
 "Age": "18",
 }
 print(dict)
 

{'Name': 'Any_name', 'Age': '18'}

Accesing values in dictionary:

To access dictionary elements, you can use the familiar square brackets along with the key to obtain its value.

dict ={
 "Name": "Any_name",
 "Age": "18",
 }
 print(dict['Name'])
 print(dict['Age'])
 # printing both values
 print(dict['Name']+"is"+dict['Age']+"years old.")
 
 

Any_name
 18
 Any_nameis18years old.

Adding,Updating ,Deleting dictionary elements:

Adding items:

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

dict ={
 "Name": "Any_name",
 "Age": "18",
 }
 dict['Address']="your_add"
 print(dict)
 

{'Name': 'Any_name', 'Age': '18', 'Address': 'your_add'}

Updating items:

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

dict ={
 "Name": "Any_name",
 "Age": "18",
 }
 dict['Age']="20"
 print(dict)
 

{'Name': 'Any_name', 'Age': '20'}

 The update() method will update the dictionary with the items from the given argument.

The argument must be a dictionary, or an iterable object with key:value pairs.

dict ={
 "Name": "Any_name",
 "Age": "18",
 }
 dict.update({"Age": 22})
 print(dict)
 

{'Name': 'Any_name', 'Age': 22}

Deleting items:

The del keyword removes the item with the specified key name:

Example:

dict ={
 "Name": "Any_name",
 "Age": "18",
 }
 del dict['Name']
 print(dict)

{'Age': '18'}
 

We can also delete the entire dictionary using del keyword.

dict ={
 "Name": "Any_name",
 "Age": "18",
 }
 del dict
 print(dict)

<class 'dict'>

Summerizing :

#creating dictionary dict
 dict ={
 "Name": "Any_name",
 "Age": "18",
 }
 print(dict)
 
 #accessing values
 print(dict['Name'])
 
 #adding items
 dict['Address']="your_add"
 print(dict)
 
 #updating items
 dict.update({"Age": 22})
 print(dict)
 
 #deleting items
 del dict['Name']
 print(dict)
 
 

{'Name': 'Any_name', 'Age': '18'}
 Any_name
 {'Name': 'Any_name', 'Age': '18', 'Address': 'your_add'}
 {'Name': 'Any_name', 'Age': 22, 'Address': 'your_add'}
 {'Age': 22, 'Address': 'your_add'}

Iterating through dictionaries in python:

we can loop through a dictionary by using a for loop.There are multiple ways to iterate over a dictionary in Python.

Iterate through all keys

Here we create a dictionary named firstand_lastname and iterate through all keys.

firstand_lastname = {
 
  'john' : 'bista',
 
  'Jeff' : 'bezos',
 
  'Suraj' : 'raaj',
 
  }
 
 
  print('firstnames:')
 
  # Iterating over keys
 
 for f_name in firstand_lastname :
 
  print(f_name)

firstnames:
 john
 Jeff
 Suraj

Iterate through all values:

firstand_lastname = {
  'john' : 'bista',
  'Jeff' : 'bezos',
  'Suraj' : 'raaj',
  'anthony' : 'charlie'
  }
 
 print('lastnames:')
 
 # Iterating over values
 for last_name in firstand_lastname.values():
  print(last_name)

In this case the values may not be printed in the order they are stored.

lastnames:
 bista
 bezos
 raaj
 charlie

Iterate through all key, value pairs:

here in this example all the key values pairs are printed.

firstand_lastname = {
  'john' : 'bista',
  'Jeff' : 'bezos',
  'Suraj' : 'raaj',
  'anthony' : 'charlie'
  }
 
 # Iterating over keys and values
 print("the complete names are:")
 
 for lname, last_name in firstand_lastname.items():
  print(lname, ":", last_name)
 

the complete names are:
 john : bista
 Jeff : bezos
 Suraj : raaj
 anthony : charlie

The link to the notebook in github repo is here .