Python Data Type: Dictionary

Creating Dictionary

# A simple Dictionary
d1 = {1: "a", 2: "b", 3: "c", 4: "d"}
d2 = {"aa": 11, 12: "bb", 13: "cc", "dd": 14}

# Empty Dictionary
empty_dict = {}

# Dictionary Comprehension
d3 = {x: x * x for x in range(20)}
# Squares of number from 0 to 19  ex: 2:4,3:9,4:16

d4 = {x: x * x * x for x in range(20) if x % 2 == 0}
# Cubes of Even Number from 0 to 19  ex: 2:8, 4:64

# Using dict function
# Creating Dictionary from list
d5 = dict([[1, 2], [3, 4], [5, 6], [7, 8]])  # {1:2, 3:4, 5:6, 7:8}

# Creating Dictionary from Tuple
d6 = dict(([1, 1], [2, 4], [3, 9]))  # {1:1, 2:4, 3:9}

# Nested Dictionary
nested = {1: "x", 2: "y", 3: {"a": 1, "e": 2, "i": 3, "o": 4, "u": 5}, 4: "z"}

Accessing Items of dictionary

Can be done using key

print(d1)
print(d1[1])
print(d2["aa"])
print(d3.get(4))
print(nested[3]["a"])

Updating Values of Dictionary

# Reassigning Values in Dictionary: 
# However, if the key doesn’t already exist in the dictionary, then it adds a new one.
d1[1] = "a1"
d2["aa"] = 111

# Adding extra key-value pairs in Dictionary
d1[5] = "e"
d1[6] = "f"
empty_dict[1] = "aeiou"

Deleting the items of the dictionary

# Deleting entire dictionary
del empty_dict

# Deleting the specific item of the dictionary
del d1[5]

In-Built Functions of Dictionary- len, any, all, sorted

# len()
print(len(d1))

# any()
print(any({False: False, "": ""}))  # Prints False
print(any({False: False, "a": 1}))  # Prints True

# all()
print(all({False: False, "": ""}))  # Prints False
print(all({False: False, "a": 1}))  # Prints False

# Sorted()
d7 = {3: "a", 2: "b", 1: "c"}
d8 = {"c": 3, "b": 2, "a": 1}
print(sorted(d7))  # Prints [1,2,3]
print(sorted(d8))  # Prints ['a','b','c']
print(type(sorted(d7)))  # Prints class 'list'

# Keys()- It returns the keys of the entire dictionary
print(d1.keys())  # Prints dict_keys([1, 2, 3, 4, 6])

# Value()- It returns the values of entire dictionary
print(d1.values())  # Prints dict_values(['a1', 'b', 'c', 'd', 'f'])

# items()- It returns the list of key-value pairs
print(d1.items())
# Prints dict_items([(1, 'a1'), (2, 'b'), (3, 'c'), (4, 'd'), (6, 'f')])

# get()- It takes one to two arguments.
# While the first is the key to search for, the second is the value to return if the key isn’t found.
# The default value for this second argument is None.
print(d1.get(1, 0))  # Prints a1
print(d1.get(5, 0))  # Returns 0 since there is not any key 5

# clear(): It clears the entire dictionary
d7.clear()
d8.clear()

# copy()- It copies the dictionary
new_dict = d1.copy()

# pop()- This method is used to remove and display an item from the dictionary.
# It takes one to two arguments.
# The first is the key to be deleted, while the second is the value that’s returned if the key isn’t found.
d7 = {1: "a", 2: "b", 3: "c", 4: "d"}
d7.pop(1)
d7.pop(2, 0)
print(d7.pop(3, 0))

# Update()-The update() method takes another dictionary as an argument.
# Then it updates the dictionary to hold values from the other dictionary that it doesn’t already.
dict1 = {1: 1, 2: 2}
dict2 = {2: 2, 3: 3}
dict1.update(dict2)
print(dict1)  # Prints {1: 1, 2: 2, 3: 3}

Python Dictionary Opeartions

# Membership
print(1 in dict1)  # Prints True
print(3 not in dict1)  # Prints True