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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

  • Iterate through all values

  • Iterate through all key, value pairs

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 .



















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