Page 170 - Computer Science V2.0 Class 11

7.1.6 Dictionary (Mapping)
A dictionary (dict) is an unordered set of key-value pairs enclosed in curly brackets:{}. It maps a set of keys to a set
of values. The key is separated from its value using a colon(:) and key-value pairs are separated from each other by
commas (,). A dictionary does not allow repeated keys.

>>> furniturePrice = {'chair':500, 'table': 2000, 'stool':1000}
>>> furniturePrice
{'chair': 500, 'table': 2000, 'stool': 1000}
>>> furniturePrice['table']
2000

For each of the following, identify its type.
1. 14.5
2. -203
3. 14+7j
4. True
5. "Python"
6. [34,'Book', 25]
7. ('Small','Medium','Large')
8. {'Small','Medium','Large'}
9. {'rollno':10,'name':'Joy'}

7.2 Mutable and Immutable DataTypes

Data types in Python are broadly categorised into two types—mutable and immutable. A modifiable object and its
associated type are called mutable. For example, lists and dictionaries are mutable. Numeric data types (int, float,
and complex), bool, str, and tuple, are immutable data types (see Fig 7.2). Next, we give examples of mutable
and immutable data objects.

>>> num1 = 50
>>> id(num1)
1734046084944
Recall that the function id() yields the object id of an object. Fig. 7.2 shows object 50 being referenced by the
variable num1.

num1 50
1734046084944

Fig 7.2: num1 pointing to the data object 50
Next, consider another assignment statement:
>>> num2 = num1
>>> id(num2)
1734046084944
Note that each of the variables num1, and num2 refers to the same object, 50 in the memory.

num1 50
1734046084944

num2

Fig 7.3: num1 and num2 pointing to the same object 50

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