Chapter 9: Problem 6

How can you determine whether a key-value pair exists in a dictionary?

Short Answer

Expert verified

Answer: You can check if a specific key-value pair exists in a Python dictionary by using the `items()` method, which returns a list of key-value tuple pairs. You can then use the `in` keyword to check if the tuple containing the specific key-value pair is present in the list. For example: ```python my_dictionary = {'john': 25, 'jane': 30, 'doe': 35} print(('john', 25) in my_dictionary.items()) # Output: True print(('jane', 40) in my_dictionary.items()) # Output: False ```

Step by step solution

Understand dictionaries in Python

In Python, a dictionary is an unordered collection of key-value pairs, separated by colons and enclosed in curly braces {}. An example of a dictionary is: my_dictionary = {'john': 25, 'jane': 30, 'doe': 35}. Here 'john', 'jane', and 'doe' are keys and 25, 30, and 35 are their respective values.

Checking if a key exists in the dictionary

In order to check if a key exists in the dictionary, you can use the `in` keyword. This keyword returns 'True' if the specified key is present in the dictionary, otherwise, it returns 'False'. Here is an example: Example: ```python my_dictionary = {'john': 25, 'jane': 30, 'doe': 35} print('john' in my_dictionary) # Output: True print('mark' in my_dictionary) # Output: False ```

Checking if a value exists in the dictionary

You can also check if a value exists in the dictionary using the `values()` method which returns a list-like object of all the values in the dictionary. Here's how it can be done: Example: ```python my_dictionary = {'john': 25, 'jane': 30, 'doe': 35} print(25 in my_dictionary.values()) # Output: True print(40 in my_dictionary.values()) # Output: False ```

Checking if a key-value pair exists in the dictionary

Finally, to check if a specific key-value pair exists in the dictionary, you can use the `items()` method which returns a list of key-value tuple pairs. You can then use the `in` keyword to check if the tuple containing the specific key-value pair is present in the list. Here's an example: Example: ```python my_dictionary = {'john': 25, 'jane': 30, 'doe': 35} print(('john', 25) in my_dictionary.items()) # Output: True print(('jane', 40) in my_dictionary.items()) # Output: False ```

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How can you determine whether a key-value pair exists in a dictionary?

Short Answer

Step by step solution

Understand dictionaries in Python

Checking if a key exists in the dictionary

Checking if a value exists in the dictionary

Checking if a key-value pair exists in the dictionary

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