Summary

Conclusions

A str is an immutable sequence of code points, while bytes represents encoded bytes. String methods are sufficient for simple cleaning and splitting; Unicode normalization is needed to compare canonically equivalent forms. F-strings produce text immediately, while t-strings preserve static parts and values for a custom processor. A regular expression checks structure, but semantic constraints on dates, amounts, and other data are checked separately.

Self-check questions

1. What exactly does len count for str and for bytes?
2. Why does replace not change the original string?
3. How do split() and split(" ") differ?
4. Why is strip(".txt") not a way to remove an extension?
5. Why is NFC normalization needed?
6. How do the purposes of casefold and lower differ?
7. What do width, precision, and type mean in a format specification?
8. When is !r useful, and when is it incompatible with a numeric format?
9. What type does a t-string create, and when are its expressions evaluated?
10. Why does the t prefix alone not guarantee HTML safety?
11. How do the two classes named Template differ?
12. When do you use search, match, and fullmatch?
13. How do capturing groups affect the findall result?
14. Why pass a function to re.sub?
15. Why does matching a regex not yet prove that a date is valid?

Useful links

• https://docs.python.org/3.14/library/stdtypes.html#text-sequence-type-str.
• https://docs.python.org/3.14/howto/unicode.html.
• https://docs.python.org/3.14/library/string.html.
• https://docs.python.org/3.14/library/string.templatelib.html.
• https://peps.python.org/pep-0750/.
• https://docs.python.org/3.14/howto/regex.html.