Meaning of Dictionary in python language

Dictionaries in Python language

1. Dictionary in python

2. 1. Dictionaries are built in data types in python 2. dictionaries are used to store the data in key : value pairs 3. Unlike other sequential data types which are indexed by a range of numbers, dictionaries are indexed by keys. 4. keys in a dictionary can be any immutable type; like strings and numbers. 5. Tuples can be used as keys if they contain only strings, numbers or tuples . 6. If a tuple contains any mutable object either directly or indirectly it cannot be used as a key.

3. 7. you can not use lists as keys, since lists can be modified in place using index assignments, slice assignments or methods like append() and extend(). 8. Mutable : We can add, remove, and change items after the dictionary has been created. 9. Dynamic Size : Dictionaries can grow and shrink as needed, as we can add or remove key value pair. 10. Efficient lookups : Dictionaries are implemented using hash tables, providing average O(1) time Complexity For lookups, insertion, and deletions.

4. 11. Flexible Value Types: Values in a Dictionary can be of any datatype, including other dictionaries, lists, sets, or even custom objects. 12. Comprehensions: Python Supports dictionary comprehensions, which allow you to create dictionaries in a concise and readable manner. 13. Methods : Dictionaries come with a variety of buit -in methods for operations like retrieving keys keys(), values(), item(),pop(). And more.

5. # Creating a Dictionary My_dict = {'name' : “Ram", "age" : 30, "City" : "new York"} print( My_dict ) #{'name': ‘Ram', 'age': 30, 'City': 'new York'} #adding a key – value pair My_dict [“job”] = “Engineer” print( My_dict ) # {'name': ‘Ram', 'age': 30, 'City': 'new York', 'job': 'Engineer’} #Modifying a value My_dict [“age”] = 31 print( My_dict ) # {'name': ‘Ram', 'age': 31, 'City': 'new York', 'job': 'Engineer’} #Removing a key value pair del My_dict [‘city’] # {'name': ‘Ram', 'age': 31, 'job': 'Engineer'} #checking if a key exists print(“name” in My- dict ) #True

6. #Iterating over keys and values For key, value in My_dict.items (): print(f”{key} : {value}”) # using a dictionary comprehension Squares = {x: x*x for x in range(5)} print(Squares)

7. Iterating over keys and values for key, value in My_dict.items (): print(f"{key} : {value}")

8. Using a dictionary comprehension quares = {x: x*x for x in range(5)} print(squares) Output: {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

9. Pop() function In Python, the pop() method in dictionaries is used to remove a specified key and return its corresponding value. If the specified key is not found, the method can return a default value if provided, or raise a KeyError if no default value is specified. dict.pop (key[, default]) key: The key to be removed from the dictionary. default (optional): The value to return if the key is not found. If not provided and the key is not found, a KeyError is raised.

10. Example # Define a dictionary my_dict = {'a': 1, 'b': 2, 'c': 3} # Remove and return the value for the key 'b' value = my_dict.pop ('b') print(value) # Output: 2 # Print the updated dictionary print( my_dict ) # Output: {'a': 1, 'c': 3}

11. # Define a dictionary my_dict = {'a': 1, 'b': 2, 'c': 3} # Attempt to remove and return the value for a non-existing key 'd' with a default value value = my_dict.pop ('d', 'Key not found') print(value) # Output: Key not found # Print the updated dictionary print( my_dict ) # Output: {'a': 1, 'b': 2, 'c': 3}

12. # Define a dictionary my_dict = {'a': 1, 'b': 2, 'c': 3} # Attempt to remove and return the value for a non-existing key 'd' with a default value value = my_dict.pop ('d') print(value) # Output: Key not found # Print the updated dictionary print( my_dict ) # Output: {'a': 1, 'b': 2, 'c': 3} Output: KeyError : ‘d’ throw an exception and stop the execution .

13. Summary The pop() method removes the specified key from the dictionary and returns its value.If the key is not found, it can return a default value if provided; otherwise, it raises a KeyError.This method is useful for safely removing and retrieving values from a dictionary.