Unit 1(Lesson7).pptx
- 1. Unit 1(Lesson7) Introduction to Dictionary
- 2. Dictionary is an unordered collection of key and value pairs. Note : While other compound data types (like lists, tuples, and sets) have only values as an element, a dictionary has a key : value pair
- 3. General usage of dictionaries is to store key-value pairs like : • Employees and their wages • Countries and their capitals • Commodities and their prices In a dictionary, the keys should be unique, but the values can change. For example, the price of a commodity may change over time, but its name will not change. Immutable data types like number, string, tuple etc. are used for the key and any data type is used for the value.
- 4. • Dictionaries are optimized to retrieve values when the keys are known. • Dictionaries are represented using key-value pairs separated by commas inside curly braces {}. The key-value pairs are represented as key : value. For example, daily temperatures in major cities are mapped into a dictionary as { "Hyderabad": 27, "Chennai": 32, "Mumbai": 40}.
- 5. • Creating a dictionary: • A dictionary can be created in two ways. oUsing the built-in dict() function. o Assigning elements directly.
- 6. • 1. Using built-in dict() function. An empty dictionary can be created as follows : mydict = dict() # Creating an empty dictionary called mydict print(type(mydict)) # Printing data type of mydict. print(mydict) # Prints empty dictionary. Output : <class 'dict'> {}
- 7. mydict = dict(Hyderabad = 20, Delhi = 30) # A dictionary with two key pairs is created. print(mydict) # Prints the dictionary Output : {'Hyderabad': 20, 'Delhi': 30} A dictionary with elements can be created as follows : Note : The two key pairs are specified in the dict() function as comma separated key = value.
- 8. • 2. Assigning elements directly. A dictionary is created using direct assignment as follows : mydict = {1:"one", 2 :"two", 3:"three"} # Create a dictionary with three key-value pairs. print(mydict) # Printing the dictionary print(type(mydict)) # will print output as follows Output : {1:"one", 2 :"two", 3:"three"} <class 'dict'>
- 9. Which of the following options are correct? Which of the following is feature of Dictionary? 1. Keys are unique within a dictionary. 2. Keys must be of an immutable data type. 3. Dictionary is mutable. 4. dictionary() function is used to create an empty dictionary. a) All options are correct b) 1,2 and 3 only c) 3 and 4 only d) 1,3 and 4 only
- 10. Which of the following options are correct? Which of the following is feature of Dictionary? 1. Keys are unique within a dictionary. 2. Keys must be of an immutable data type. 3. Dictionary is mutable. 4. dictionary() function is used to create an empty dictionary. a) All options are correct b) 1,2 and 3 only c) 3 and 4 only d) 1,3 and 4 only