When to Use %r Instead of %s in Python

In this article, we’ll explain when to use %r instead of %s in Python, and the differences between them. In Python, both %r and %s are used to format strings. The main difference between them lies in how they handle different types of objects.

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The Difference Between %r and %s

%r and %s are both string formatting operators, used to insert the value of a variable into another string. The difference between the two is that %r uses the repr() function to represent the variable’s value in the result, while %s uses the str() function.

The repr() function returns a string containing the object in a way that can be recreated in the interpreter. It typically returns a quoted string and escapes special characters.

The str() function returns a more human-readable string representation. It does not include quotes or escape special characters.

When to Use %r

Here are some situations where you should use %r:
– When you need to display the full representation of an object in a string, regardless of its type.
– When you need to debug code and see the values of special, escaped, or non-ASCII characters.

Let’s look at some examples to illustrate when to use %r.

name = "Alice"
print("Hello, %r!" % name)

The output will be Hello, 'Alice'!. In this example, we use %r to display the full representation of the variable name, including the quotes.

age = 25
print("I am %r years old." % age)

The output will be I am 25 years old.. Here, we use %r to display the value of the variable age, rather than using %s. While both output the same value in this example, using %r better expresses the variable’s type.

info = {"name": "Bob", "age": 30}
print("Information: %r" % info)

The output will be Information: {'name': 'Bob', 'age': 30}. In this example, we use %r to display the complete representation of the dictionary info, including the braces and quotes.

When to Use %s

Here are some situations where you should use %s:
– When you need to display a readable string to the user, especially when you don’t need to display the full representation of the object.
– When you need to convert an object to a string and pass it to a function that accepts a string as an argument.

Let’s look at some examples to illustrate when to use %s.

name = "Alice"
print("Hello, %s!" % name)

The output will be Hello, Alice!. In this example, we use %s to display a human-readable string representation of the variable name, without the quotes.

age = 25
print("I am %s years old." % age)

The output will be I am 25 years old.. Here, we use %s to display the value of the variable age, rather than using %r. Although both produce the same output in this example, using %s is more appropriate in this case because we only want to display a human-readable string.

info = {"name": "Bob", "age": 30}
print("Information: %s" % info)

The output will be Information: {'name': 'Bob', 'age': 30}. In this example, we use %s to display a human-readable string representation of the dictionary info, without the braces and quotes.

Summary

In Python, %r and %s are both operators used to format strings. The difference between them lies in the functions they use: repr() and str(), respectively. %r returns a string representation used by the interpreter to recreate the object, while %s returns a human-readable string representation.

Use %r when you need to display the full representation of an object in a string. Use %s when you need to display a readable string to the user or convert an object to a string and pass it to a function that accepts a string as an argument.

I hope this article helps you understand the difference between %r and %s. In real-world programming, choosing the appropriate formatting operator can make your code clearer and easier to read.