Python Regex Character Classes and Quantifiers

Match digit, letter, and whitespace classes with quantifiers.

How It Works

Character classes such as [A-Z] or \d select characters, while *, +, ? and {n,m} control repetition. By default, shorthand classes can include non-ASCII Unicode characters; use re.ASCII when ASCII-only behavior is required.

Step-by-Step Example

import re
text = 'SKU-4827'
print(re.findall(r'[A-Z]+|\d+', text))
print(bool(re.fullmatch(r'[A-Z]{3}-\d{4}', text)))

Understanding the Example

The expression "'SKU-4827'" supplies the value stored as 'text'. This value is then used or checked by the later statements.
The print() call exposes the result so you can compare it with the behavior described above. Check the value and its type when experimenting.

A successful run of this example prints the following output:

['SKU', '4827']
True

Where This Fits in a Real Program

Start by writing down examples that should match and examples that must fail. Check whether you need to locate a substring, match a prefix or validate an entire field; these are different operations. Unicode and escape sequences can also change which characters are matched, so test accented text and empty input.

Practice: Try It Yourself

Validate complete input with fullmatch() rather than a partial search.

For this exercise, predict the result before running the changed code. Then explain the difference between the original and modified cases using the actual values, not just whether the program completed.

Common Beginner Mistakes

Using \d when ASCII digits are required or forgetting to escape special punctuation.
Write a pattern that recognizes a two-letter code followed by three digits.

Key Takeaways

Match digit, letter, and whitespace classes with quantifiers.
Character classes such as [A-Z] or \d select characters, while *, +, ? and {n,m} control repetition.
Apply the demonstrated operation to the practice input and verify its result before depending on it in a larger program.