When to use %r instead of %s in Python?

In Python, string formatting can be done using the % formatting operator. The %s uses str() to convert values, while %r uses repr() to convert values. Understanding when to use each is crucial for debugging and logging.

Key Differences

• %s: Converts the value to a human-readable string using str()
• %r: Converts the value to its representation using repr(), showing quotes, escape characters, etc.

When to Use %r

Use %r when you need to see the exact representation of a value, including escape characters, quotes, and whitespace. This is particularly useful for:

• Debugging strings with hidden characters
• Logging exact values
• Understanding data structure contents

Example 1: Handling Escape Characters

Here we compare how %s and %r handle newline characters ?

text = "TP\nTutorialsPoint"
print("Using %%s: %s" % text)
print("Using %%r: %r" % text)

Using %s: TP
TutorialsPoint
Using %r: 'TP\nTutorialsPoint'

Notice how %s interprets the newline while %r shows the raw escape sequence.

Example 2: Debugging Whitespace Issues

When debugging strings with leading/trailing spaces, %r makes them visible ?

text = "  TutorialsPoint "
print("Using %%s: %s" % text)
print("Using %%r: %r" % text)

Using %s:   TutorialsPoint 
Using %r: '  TutorialsPoint '

The %r clearly shows the surrounding quotes and spaces that might be invisible with %s.

Example 3: Data Structures

For data structures without special characters, both operators produce similar output ?

cars = ["RX100", "Ciaz", "Chiron"]
print("Using %%s: %s" % cars)
print("Using %%r: %r" % cars)

Using %s: ['RX100', 'Ciaz', 'Chiron']
Using %r: ['RX100', 'Ciaz', 'Chiron']

Practical Use Cases

Conclusion

Use %r for debugging and logging when you need to see the exact representation of values. Use %s for user-friendly display and general string formatting.