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Python Dictionary

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Python Dictionary

Table Of Contents:

  • What Is A Dictionary?
  • How To Create A Python Dictionary?
  • Accessing Dictionary Elements.
  • Looping Through Dictionary.
  • Adding Elements To Dictionary.
  • Updating Values In Dictionary.
  • Removing Items From Dictionary.
  • Copying A Dictionary.
  • Deleting A Dictionary.

(1) What Is A Dictionary?

  • Dictionaries are used to store data in key:value pairs.
  • Key is used to uniquely identify each value.
  • Dictionary preserves the order of the elements stored.
  • Dictionary do not allow duplicate elements to store.
  • Dictionary is mutable in nature, that means we can add,remove or update the values of
  • Dictionary without creating a new memory location.

(2) How To Create A Dictionary?

  • Dictionaries are written using curly brackets { }.
  • Elements of the dictionary will be Key : Value pairs separated by comma ( , ).

Example-1

dict1 = {
    "Name": "Subrat",
    "Roll No": 16783,
    "Subject":"Math",
    "Percentage":95
}

print(dict1)
Output:
{'Name': 'Subrat', 'Roll No': 16783, 'Subject': 'Math', 'Percentage': 95}

Example-2

dict2 = {
    "Name": "Abhispa Pattnaik",
    "Address":'Odisha,India',
    "Pin":654786,
    "Land Mark":'Near Bank'
}

print(dict2)
Output:
{'Name': 'Abhispa Pattnaik', 'Address': 'Odisha,India', 'Pin': 654786, 'Land Mark': 'Near Bank'}

Note:

  • Here both key and values are variables. You have to write them as per the variable rules.
  • In both the examples I have taken key as a String type.

(3) Accessing Dictionary Elements?

  • You can access the items of a dictionary by referring to its key name, inside square brackets.
  • There is also a method called get() that will give you the same result.

Example-1: Using Keys

dict1 = {
    "Name": "Abhispa Pattnaik",
    "Address":'Odisha,India',
    "Pin":654786,
    "Land Mark":'Near Bank'
}

print(dict1['Name'])
print(dict1['Address'])
print(dict1['Pin'])
print(dict1['Land Mark'])
Output:
Abhispa Pattnaik
Odisha,India
654786
Near Bank

Example-2: get() Method

dict2 = {
    "Name": "Abhispa Pattnaik",
    "Address":'Odisha,India',
    "Pin":654786,
    "Land Mark":'Near Bank'
}

print(dict2.get("Name"))
print(dict2.get("Address"))
print(dict2.get("Pin"))
print(dict2.get("Land Mark"))
Output:
Abhispa Pattnaik
Odisha,India
654786
Near Bank

(4) Looping 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.
  • keys() method will return you all the Keys of the Dictionary.
  • values() method will return you all the values of the Dictionary.
  • items() method will return you both key and values of the Dictionary.

Example-1: Printing Keys Of The Dictionary

thisdict = {
    "Name": "Abhispa Pattnaik",
    "Address":'Odisha,India',
    "Pin":654786,
    "Land Mark":'Near Bank'
}

for val in thisdict:
    print(val)
Output:
Name
Address
Pin
Land Mark

Note:

  • Here val will contains keys of the Dictionary.
  • By using key you can access the values of the Dictionary using square bracket [ ].

Example-2: Printing Values Of The Dictionary

thisdict = {
    "Name": "Abhispa Pattnaik",
    "Address":'Odisha,India',
    "Pin":654786,
    "Land Mark":'Near Bank'
}

for val in thisdict:
    print(thisdict[val])
Output:
Abhispa Pattnaik
Odisha,India
654786
Near Bank

Example-3: Using keys() Method

thisdict = {
    1:'Yudhishtira',
    2:'Bhima',
    3:'Arjuna',
    4:'Nakula',
    5:'Sahadeva'
}

for keys in thisdict.keys():
    print(keys)
Output:
1
2
3
4
5

Example-4: Using values() Method

thisdict = {
    1:'Yudhishtira',
    2:'Bhima',
    3:'Arjuna',
    4:'Nakula',
    5:'Sahadeva'
}

for values in thisdict.values():
    print(values)
Output:
Yudhishtira
Bhima
Arjuna
Nakula
Sahadeva

Example-5: Using items() Method

thisdict = {
    1:'Yudhishtira',
    2:'Bhima',
    3:'Arjuna',
    4:'Nakula',
    5:'Sahadeva'
}

for key, value in thisdict.items():
    print('Key:',key)
    print('Value:',value)
Output:
Key: 1
Value: Yudhishtira
Key: 2
Value: Bhima
Key: 3
Value: Arjuna
Key: 4
Value: Nakula
Key: 5
Value: Sahadeva

(5) Adding New Items To A Dictionary

  • You can add new item by using new key name and assigning a value to it.
  • update( ) method will update the original Dictionary element to a new value. If the item does not exist, the new item will be added.
  • For update( ) method the argument must be a dictionary, or an iterable object with key:value pairs.

Example-1: Using key and value

thisdict = {
    1:'India',
    2:'USA',
    3:'France',
    4:'Finland',
    5:'Ireland'
}

print('Before',thisdict)

thisdict[6] = 'Poland' #You Can Update By Using A New Key 

print('After',thisdict)
Output:
Before {1: 'India', 2: 'USA', 3: 'France', 4: 'Finland', 5: 'Ireland'}
After {1: 'India', 2: 'USA', 3: 'France', 4: 'Finland', 5: 'Ireland', 6: 'Poland'}

Example-2: Using update() Method

thisdict = {
    1:'India',
    2:'USA',
    3:'France',
    4:'Finland',
    5:'Ireland'
}

print('Before',thisdict)

thisdict.update({6:'Poland'}) #Using Update Method.

print('After',thisdict)
Output:
Before {1: 'India', 2: 'USA', 3: 'France', 4: 'Finland', 5: 'Ireland'}
After {1: 'India', 2: 'USA', 3: 'France', 4: 'Finland', 5: 'Ireland', 6: 'Poland'}

(6) Updating Values To A Dictionary

  • update( ) method will update the original Dictionary element to a new value. If the item does not exist, the new item will be added.
  • For update( ) method the argument must be a dictionary, or an iterable object with key:value pairs.

Example-1: Updation Using Key : Value Pair

thisdict = {
    'Rank1':'Subrat',
    'Rank2':'Abhipsha',
    'Rank3':'Smita',
    'Rank4':'Suchitra',
    'Rank5':'Monalisa',
}

print('Before',thisdict)

thisdict['Rank6'] = 'Aradhna' #You Can Update By Using A New Key 

print('After',thisdict)
Output:
Before {'Rank1': 'Subrat', 'Rank2': 'Abhipsha', 'Rank3': 'Smita', 'Rank4': 'Suchitra', 'Rank5': 'Monalisa'}
After {'Rank1': 'Subrat', 'Rank2': 'Abhipsha', 'Rank3': 'Smita', 'Rank4': 'Suchitra', 'Rank5': 'Monalisa', 'Rank6': 'Aradhna'}

Example-2: Using update( ) Method

thisdict = {
    'Rank1':'Subrat',
    'Rank2':'Abhipsha',
    'Rank3':'Smita',
    'Rank4':'Suchitra',
    'Rank5':'Monalisa',
}


print('Before',thisdict)

thisdict.update({'Rank6':'Aradhna'}) #Using Update Method. 

print('After',thisdict)
Output:
Before {'Rank1': 'Subrat', 'Rank2': 'Abhipsha', 'Rank3': 'Smita', 'Rank4': 'Suchitra', 'Rank5': 'Monalisa'}
After {'Rank1': 'Subrat', 'Rank2': 'Abhipsha', 'Rank3': 'Smita', 'Rank4': 'Suchitra', 'Rank5': 'Monalisa', 'Rank6': 'Aradhna'}

Example-3: Updating Existing Key

thisdict = {
    'Rank1':'Subrat',
    'Rank2':'Abhipsha',
    'Rank3':'Smita',
    'Rank4':'Suchitra',
    'Rank5':'Monalisa',
}


print('Before',thisdict)

thisdict.update({'Rank5':'Aradhna'}) #Using Update Method. 

print('After',thisdict)
Output:
Before {'Rank1': 'Subrat', 'Rank2': 'Abhipsha', 'Rank3': 'Smita', 'Rank4': 'Suchitra', 'Rank5': 'Monalisa'}
After {'Rank1': 'Subrat', 'Rank2': 'Abhipsha', 'Rank3': 'Smita', 'Rank4': 'Suchitra', 'Rank5': 'Aradhna'}

Note:

  • Here ‘Rank5′:’Monalisa’ has updated to ‘Rank5’: ‘Aradhna’.
  • If you are updating the existing key value then, it’s value will be updated to new value.

(7) Removing Items From Dictionary.

  • The pop() method removes the item with the specified key name. And return the value which is removed.
  • The pop() method takes dictionary key as its argument.
  • The popitem() method removes the last inserted item (in versions before 3.7, a random item is removed instead).
  • The del keyword removes the item with the specified key name.
  • The del keyword can also delete the dictionary completely.
  • The clear() method empties the dictionary.

Example-1: Using pop() Method

thisdict = {
    1:'Math',
    2:'Science',
    3:'English',
    4:'History',
    5:'Geography',
    6:'Economics',   
}

print('Before',thisdict)

popped = thisdict.pop(4)

print(popped)

print('After',thisdict)
Output:
Before {1: 'Math', 2: 'Science', 3: 'English', 4: 'History', 5: 'Geography', 6: 'Economics'}
History
After {1: 'Math', 2: 'Science', 3: 'English', 5: 'Geography', 6: 'Economics'}

Example-2: Using popitem() Method

thisdict = {
    1:'Math',
    2:'Science',
    3:'English',
    4:'History',
    5:'Geography',
    6:'Economics',   
}

print('Before',thisdict)

popped = thisdict.popitem()

print(popped)

print('After',thisdict)
Output:
Before {1: 'Math', 2: 'Science', 3: 'English', 4: 'History', 5: 'Geography', 6: 'Economics'}
(6, 'Economics')
After {1: 'Math', 2: 'Science', 3: 'English', 4: 'History', 5: 'Geography'}

Example-3: Using del Keyword

thisdict = {
    1:'Math',
    2:'Science',
    3:'English',
    4:'History',
    5:'Geography',
    6:'Economics',   
}

print('Before',thisdict)

del thisdict[3] #Deleating A Specefic Key.

print('After',thisdict)
Output:
Before {1: 'Math', 2: 'Science', 3: 'English', 4: 'History', 5: 'Geography', 6: 'Economics'}
After {1: 'Math', 2: 'Science', 4: 'History', 5: 'Geography', 6: 'Economics'}

Example-4: Using clear() Method

thisdict = {
    1:'Math',
    2:'Science',
    3:'English',
    4:'History',
    5:'Geography',
    6:'Economics',   
}

print('Before',thisdict)

thisdict.clear()

print('After',thisdict)
Output:
Before {1: 'Math', 2: 'Science', 3: 'English', 4: 'History', 5: 'Geography', 6: 'Economics'}
After {}

(8) Copying 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.
  • You can use inbuilt copy() method to copy the dictionary.

Example-1

thisdict = {
    'table':'chair',
    'laptop':'mouse',
    'paper':'pen',
    'mobile':'charger',
    'water':'life'
}

mydict = thisdict.copy()

print(thisdict)

print(mydict)
Output:
{'table': 'chair', 'laptop': 'mouse', 'paper': 'pen', 'mobile': 'charger', 'water': 'life'}
{'table': 'chair', 'laptop': 'mouse', 'paper': 'pen', 'mobile': 'charger', 'water': 'life'}

(9) Deleting A Dictionary.

  • You can use del keyword to delete a dictionary.

Example-1

thisdict = {
    2:4,
    3:9,
    4:16,
    5:25,
    6:36
}

del thisdict

print(thisdict)
Output:
NameError                                 Traceback (most recent call last)
Input In [39], in <cell line: 11>()
      1 thisdict = {
      2     2:4,
      3     3:9,
   (...)
      6     6:36
      7 }
      9 del thisdict
---> 11 print(thisdict)

NameError: name 'thisdict' is not defined

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