Page 434 - Computer Science V2.0 Class 11

Let's Summarise

Ø A dictionary is an unordered set of key:value pairs.
Ø A dictionary may be specified by enclosing the key:value airs in braces { }.
Ø An empty pair of braces denotes an empty dictionary.
Ø Dictionary Methods: Python provides several methods for manipulating the dictionaries. These methods are
as follows:
o myDict.keys(): returns a dict_keys object comprising the set of keys included in the dictionary.
o myDict.values(): returns a dict_values object comprising the set of values included in the
dictionary.
o myDict.items(): returns a dict_items object comprising the set of items included in the dictionary.
o myDict.update(): used to add some key-value pairs to an existing dictionary.
o myDict.pop(myKey): removes the item with the specified key.
o myDict.popitem(): removes the last inserted item from the dictionary.

o myDict.clear(): method empties the dictionary.
o myDict.sorted(): used to sort by the keys or by the values.
o myDict.get(myKey): returns the value of the item with the specified key.
o myDict.copy(): returns a copy of the dictionary.
o myDict.fromkeys(keys, value): returns a dictionary with the specified keys and the specified value.
o myDict. setdefault(key, [value]): returns the value of the item with the specified key.
Ø del statement can also be used to remove key-value pair(s) from a dictionary.

Solved Exercises

A. Multiple Choice Questions.
1. Which of the following statements will delete a key-value pair for the key 'tue' in the following dictionary?
days = {'sun':1,'mon':2,'tue':3,'wed':4,'thur':5}
a. delete days['tue']
b. del.days['tue']
c. del days['tue']
d. days.del['tue']
2. Which of the following will display the keys in the dictionary myDict?
a. myDict.keys()
b. keys(myDict)
c. myDict.key()
d. print(myDict.key())
3. Consider the following dictionary:
numSquares = {1:1, 2:4, 3:9, 4:16, 5:25}
Which of the following will delete the key:value pair 2:4
a. del numSquares[2:4]
b. del numSquares[2]
c. numSquares.remove(2)
d. numSquares.remove(2:4)
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