Use anchors, word boundaries, and capture groups to specify match positions.
How It Works
^ and $ assert boundaries (with MULTILINE nuances), locates a word boundary, and parentheses capture subexpressions. A capturing group changes the output shape of findall(); use (?:...) for grouping without capture.
Step-by-Step Example
import re
message = 'Code: XY-42'
matched_code = re.search(r'\b([A-Z]{2})-(\d{2})\b', message)
print(matched_code.groups() if matched_code else None)Understanding the Example
- The expression "'Code: XY-42'" supplies the value stored as 'message'. This value is then used or checked by the later statements.
- The expression "re.search(r'\\b([A-Z]{2})-(\\d{2})\\b', message)" supplies the value stored as 'matched_code'. This value is then used or checked by the later statements.
A successful run of this example prints the following output:
('XY', '42')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
Use fullmatch() when a whole value must conform to a format.
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.
Further Reading
Read the official Python documentation for complete parameters, return types and exceptions.
Common Beginner Mistakes
- Assuming means a literal space or overlooking group-number shifts after adding parentheses.
- Extract a two-letter prefix and numeric suffix using groups.
Key Takeaways
- Use anchors, word boundaries, and capture groups to specify match positions.
- ^ and $ assert boundaries (with MULTILINE nuances), locates a word boundary, and parentheses capture subexpressions.
- Apply the demonstrated operation to the practice input and verify its result before depending on it in a larger program.