Chapter 9, Problem 1MC

You can use the __________ operator to determine whether a key exists in a dictionary.

a. &

b. in

c. ^

d. ?

Program Description Answer

The “in” operator is used to check that key exists in the dictionary.

 Hence, the correct answer is option “B”.

Explanation of Solution

Operator “in”:

• In Python dictionary, an “in” operator can be used to check if a key exists in the dictionary.
• The “in” operator returns true if the key exists in the dictionary.
• Otherwise, the “in” operator returns false.

Syntax:

In Python, the “in” operator can be expressed as follows:

key in dictionary_name

In the above syntax,

• The “dictionary_name” refers to the dictionary.
• The “key” represents the key to be searched in the dictionary.

Example program:

# Create a dictionary Student

Student={'Joanne':'CS-1234','Chris':'CS-1235','Jacob':'CS-1236'}

# Check if Joanne exists in the dictionary

if 'Joanne'in Student:

         # Print the value corresponding to key 'Chris'

         print("Value corresponding to key Joanne: " +Student['Joanne'])

Explanation:

In the above Python code, the first line creates a new dictionary “Student” with key-value pair elements “Joanne:CS-1234”, “Chris:1235”, and “Jacob:CS-1236”. The second line checks if the key “Joanne” exists in the dictionary “Student”. The third line prints the value corresponding to “Joanne” if the key “Joanne” exists in the dictionary “Student”.

Explanation for incorrect options:

Operator “&”:

In Python, the “&” operator is used for bitwise “And”.

Hence, option “A” is wrong.

Operator “^”:

In Python, the “^” operator is used for bitwise “Exclusive Or”.

Hence, option “C” is wrong.

Operator “?”:

The “?” is not a built- in operator in Python.

Hence, option “D” is wrong.

Sample Output

Output:

Value corresponding to key Joanne: CS-1234