Dictionaries

Overview

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Objectives

• To understand the concept of dictionaries

What are Dictionaries?

A dictionary is a datatype that stores data in key value pairs. The key and value have a colon between them(:) and the key:value pairs are seperated by “,” It is ordered*, changeable and do not allow duplicates.

Creating a Dictionary

We create a dictionary using curly({}) brackets.

pantry={'eggs':10,'butter(tbsp)':20,'sugar(oz)':30,'salt(oz)':40}

print(pantry)

Accessing elements in a Dictionary

We can access elements using the key:

print(pantry['eggs'])

keys(): The keys method returns a list of all the keys in a dictionary

k= pantry.keys()
print(k)

Inserting/changing items in a Dictionary:

We can change items using the key. There is also an update() methos that takes a dictionary as an argument to change the values.

pantry['eggs']=50
pantry.update({'eggs':10})

We can also add new elements to a dictionary in the same way:

pantry['Flour']=50
pantry.update({'pepper':60,'olive oil':70})

Copying a Dictionary:

We can use the copy() method and the dict() function. We cannot simply do dictionary1=dictionary2 as it will only create a reference instead of copying the dictionary.

pantry_copy_1=pantry.copy()
pantry_copy_2=dict(pantry)

Deletion in Dictionaries:

We use the pop() method and the del keyword to delete elements in dictionaries. We pass the key as an argument to indicate the value to be deleted

pantry.pop('olive oil')
del pantry['pepper']

the del keyword can delete the dictionary completely:

del pantry
print(pantry)

The clear() method is used to empty the dictionary.

pantry.clear()

The concept of nested Dictionaries:

A dictionary can dictionaries within itself. This is called a nested dictionary:

pantry = {
  "Pancakes" : {
    "Flour" : 6,
    "milk" : 2,
    "Eggs": 3
    "Butter" : 6
  },
  "French_toast" : {
    "Bread" : "2",
    "Eggs" : 2,
    "Sugar" : 3
    "milk" :1
  },
}
# or we can also do the following:

Pancakes = {
    "Flour" : 6,
    "milk" : 2,
    "Eggs": 3
    "Butter" : 6
  }
French_toast = {
    "Bread" : "2",
    "Eggs" : 2,
    "Sugar" : 3
    "milk" :1
  }
pantry_2 = {
  "Pancakes" : letters,
  "French_toast" : capital_letters
}

Applications of Dictionaries

• Used in Dataframes(Handling data from datasets)

Key Points