How to Check If a Dictionary Contains a Specific Value in Python

Introduction

In this lab, you will learn how to check if a Python dictionary contains a specific value. The lab begins by introducing dictionary values and demonstrating how to access them using keys and the .values() method. You'll create a dictionary_example.py file in your ~/project directory and execute Python code to print dictionary values, both individually and as a collection.

The lab then guides you through using the in operator on the values() view object to efficiently determine if a particular value exists within the dictionary. Finally, it explores an alternative approach using iteration to find matches, providing a comprehensive understanding of different methods for value checking in Python dictionaries.

Skills Graph

Understand Dictionary Values

In this step, you will learn about dictionary values in Python. Dictionaries are a fundamental data structure that store data in key-value pairs. Understanding how to access and manipulate these values is crucial for working with dictionaries effectively.

First, let's create a simple dictionary:

## Create a dictionary
my_dict = {"name": "Alice", "age": 30, "city": "New York"}

## Print the dictionary
print(my_dict)

Create a file named dictionary_example.py in your ~/project directory using the VS Code editor. Copy and paste the above code into the file.

Now, run the script using the following command in the terminal:

python dictionary_example.py

You should see the following output:

{'name': 'Alice', 'age': 30, 'city': 'New York'}

To access the values in a dictionary, you can use the keys. For example, to access the value associated with the key "name", you would use my_dict["name"].

Let's modify the dictionary_example.py file to access and print the values:

## Create a dictionary
my_dict = {"name": "Alice", "age": 30, "city": "New York"}

## Access and print the values
print(my_dict["name"])
print(my_dict["age"])
print(my_dict["city"])

Save the changes to dictionary_example.py and run it again:

python dictionary_example.py

The output should now be:

Alice
30
New York

You can also use the .values() method to get a collection of all the values in the dictionary. This method returns a view object that displays a list of all the values in the dictionary.

Modify the dictionary_example.py file to use the .values() method:

## Create a dictionary
my_dict = {"name": "Alice", "age": 30, "city": "New York"}

## Get the values
values = my_dict.values()

## Print the values
print(values)

Save the changes to dictionary_example.py and run it again:

python dictionary_example.py

The output should now be:

dict_values(['Alice', 30, 'New York'])

As you can see, the .values() method returns a view object containing all the values in the dictionary. You can iterate over this view object to access each value individually, which you will learn in the next steps.

Use in Operator on values()

In this step, you will learn how to use the in operator to check if a specific value exists within the values of a dictionary. The in operator is a powerful tool for searching and validating data in Python.

Continuing from the previous step, let's use the same dictionary my_dict. We will check if the value "Alice" exists in the dictionary's values.

Modify the dictionary_example.py file in your ~/project directory to include the following code:

## Create a dictionary
my_dict = {"name": "Alice", "age": 30, "city": "New York"}

## Check if "Alice" is in the values
if "Alice" in my_dict.values():
    print("Alice is in the dictionary values")
else:
    print("Alice is not in the dictionary values")

Save the changes to dictionary_example.py and run it again:

python dictionary_example.py

The output should be:

Alice is in the dictionary values

Now, let's check for a value that does not exist in the dictionary, such as "Bob":

Modify the dictionary_example.py file to check for "Bob" instead of "Alice":

## Create a dictionary
my_dict = {"name": "Alice", "age": 30, "city": "New York"}

## Check if "Bob" is in the values
if "Bob" in my_dict.values():
    print("Bob is in the dictionary values")
else:
    print("Bob is not in the dictionary values")

Save the changes to dictionary_example.py and run it again:

python dictionary_example.py

The output should now be:

Bob is not in the dictionary values

The in operator is case-sensitive. Let's check if "alice" (lowercase) is in the dictionary values:

Modify the dictionary_example.py file to check for "alice":

## Create a dictionary
my_dict = {"name": "Alice", "age": 30, "city": "New York"}

## Check if "alice" is in the values
if "alice" in my_dict.values():
    print("alice is in the dictionary values")
else:
    print("alice is not in the dictionary values")

Save the changes to dictionary_example.py and run it again:

python dictionary_example.py

The output should now be:

alice is not in the dictionary values

This demonstrates that the in operator is case-sensitive and will only return True if the exact value is found.

Iterate to Find Matches

In this step, you will learn how to iterate through the values of a dictionary and find matches based on specific criteria. This is a common task when you need to process or filter data stored in dictionaries.

Continuing from the previous steps, let's use the same dictionary my_dict. We will iterate through the values and print only those that are strings.

Modify the dictionary_example.py file in your ~/project directory to include the following code:

## Create a dictionary
my_dict = {"name": "Alice", "age": 30, "city": "New York"}

## Iterate through the values
for value in my_dict.values():
    ## Check if the value is a string
    if isinstance(value, str):
        print(value)

Save the changes to dictionary_example.py and run it again:

python dictionary_example.py

The output should be:

Alice
New York

In this example, we used a for loop to iterate through each value in the dictionary's values. Inside the loop, we used the isinstance() function to check if the value is a string. If it is, we print the value.

Now, let's modify the code to find values that are greater than 25. Since the age is an integer, we can check if it's greater than 25.

Modify the dictionary_example.py file to include the following code:

## Create a dictionary
my_dict = {"name": "Alice", "age": 30, "city": "New York"}

## Iterate through the values
for value in my_dict.values():
    ## Check if the value is an integer and greater than 25
    if isinstance(value, int) and value > 25:
        print(value)

Save the changes to dictionary_example.py and run it again:

python dictionary_example.py

The output should now be:

30

This demonstrates how you can combine iteration with conditional statements to find specific matches within the values of a dictionary. You can adapt this approach to different data types and criteria to suit your needs.

Summary

In this lab, you learned about dictionary values in Python, a fundamental data structure that stores data in key-value pairs. You created a dictionary and accessed its values using keys, printing the associated values for "name", "age", and "city".

Furthermore, you explored the .values() method, which returns a view object containing all the dictionary's values. You modified the script to utilize this method and print the collection of values.