How to Check If a Set Contains Only Strings in Python

Introduction

In this lab, you will learn how to check if a set in Python contains only strings. We'll start by exploring the fundamentals of string sets, including their creation, the uniqueness of elements, and common set operations like union and intersection. You'll create a string_sets.py file in the ~/project directory and use the python command to execute the code snippets, observing how sets handle duplicate entries and perform set operations.

The lab will then guide you through using the all() function with isinstance() to verify that all elements within a set are indeed strings. Finally, you'll learn how to handle empty sets and ensure your code gracefully manages this edge case when checking for string-only sets.

Skills Graph

Learn About String Sets

In this step, you will learn about string sets in Python. A set is an unordered collection of unique elements. This means that a set cannot contain duplicate values. Sets are useful for performing mathematical set operations like union, intersection, and difference. In this lab, we will focus on sets containing strings.

First, let's create a simple set of strings. Open the VS Code editor in the LabEx environment. Create a new file named string_sets.py in the ~/project directory.

## ~/project/string_sets.py
string_set = {"apple", "banana", "cherry"}
print(string_set)

Save the file. Now, run the script using the python command in the terminal:

python ~/project/string_sets.py

You should see the following output (the order of elements may vary because sets are unordered):

{'cherry', 'banana', 'apple'}

Now, let's add a duplicate element to the set and see what happens:

## ~/project/string_sets.py
string_set = {"apple", "banana", "cherry", "apple"}
print(string_set)

Save the file and run it again:

python ~/project/string_sets.py

The output will be:

{'cherry', 'banana', 'apple'}

Notice that the duplicate "apple" was automatically removed. Sets only store unique elements.

Next, let's explore some common set operations. We'll create two sets and perform union and intersection operations.

## ~/project/string_sets.py
set1 = {"apple", "banana", "cherry"}
set2 = {"banana", "date", "fig"}

## Union of two sets
union_set = set1.union(set2)
print("Union:", union_set)

## Intersection of two sets
intersection_set = set1.intersection(set2)
print("Intersection:", intersection_set)

Save the file and run it:

python ~/project/string_sets.py

The output will be:

Union: {'cherry', 'banana', 'date', 'apple', 'fig'}
Intersection: {'banana'}

The union of the two sets contains all unique elements from both sets. The intersection contains only the elements that are common to both sets.

Apply all() with isinstance()

In this step, you will learn how to use the all() function in combination with isinstance() to check if all elements in a set are strings.

The all() function returns True if all elements in an iterable (like a set) are true. If any element is false, all() returns False.

The isinstance() function checks if an object is an instance of a particular class. In our case, we'll use it to check if each element in the set is a string.

Let's start by creating a set containing only strings. Open the string_sets.py file in the ~/project directory using the VS Code editor. Modify the file to include the following code:

## ~/project/string_sets.py
string_set = {"apple", "banana", "cherry"}

## Check if all elements are strings
all_strings = all(isinstance(item, str) for item in string_set)
print("Are all elements strings?", all_strings)

Save the file. Now, run the script using the python command in the terminal:

python ~/project/string_sets.py

You should see the following output:

Are all elements strings? True

This confirms that all elements in the set are strings.

Now, let's add a non-string element (e.g., an integer) to the set and see what happens:

## ~/project/string_sets.py
string_set = {"apple", "banana", "cherry", 123}

## Check if all elements are strings
all_strings = all(isinstance(item, str) for item in string_set)
print("Are all elements strings?", all_strings)

Save the file and run it again:

python ~/project/string_sets.py

The output will be:

Are all elements strings? False

As expected, the all() function returns False because not all elements in the set are strings.

This technique is useful for validating data and ensuring that a set contains only elements of a specific type.

Check for Empty Sets

In this step, you will learn how to check if a set is empty in Python. An empty set is a set that contains no elements.

Checking for empty sets is a common task in programming, especially when dealing with data processing or conditional logic.

To create an empty set, you can use the set() constructor without any arguments. Let's modify the string_sets.py file in the ~/project directory using the VS Code editor to include the following code:

## ~/project/string_sets.py
empty_set = set()

## Check if the set is empty
if not empty_set:
    print("The set is empty")
else:
    print("The set is not empty")

Save the file. Now, run the script using the python command in the terminal:

python ~/project/string_sets.py

You should see the following output:

The set is empty

This confirms that the set empty_set is indeed empty.

Now, let's create a non-empty set and check if our logic still works:

## ~/project/string_sets.py
non_empty_set = {"apple", "banana", "cherry"}

## Check if the set is empty
if not non_empty_set:
    print("The set is empty")
else:
    print("The set is not empty")

Save the file and run it again:

python ~/project/string_sets.py

The output will be:

The set is not empty

As expected, the code correctly identifies that the set is not empty.

Another way to check if a set is empty is to use the len() function, which returns the number of elements in the set. If the length is 0, the set is empty.

## ~/project/string_sets.py
empty_set = set()

## Check if the set is empty using len()
if len(empty_set) == 0:
    print("The set is empty")
else:
    print("The set is not empty")

Save the file and run it:

python ~/project/string_sets.py

The output will be:

The set is empty

This demonstrates an alternative method for checking if a set is empty.

Summary

In this lab, you learned about string sets in Python, which are unordered collections of unique elements. You created a string set, observed that duplicate elements are automatically removed, and explored common set operations like union and intersection. The lab demonstrated how to define sets of strings and perform basic operations to understand their behavior and characteristics.

The lab also covered how to create a Python script, save it in the ~/project directory, and execute it using the python command in the terminal. You observed the output of set operations, noting that the order of elements may vary due to the unordered nature of sets.