Chapter 6 - Manipulating Strings https://automatetheboringstuff.com/2e/chapter6/
Appendix B - Running Programs https://automatetheboringstuff.com/2e/appendixb/
Chapter 7 - Pattern Matching With Regular Expressions (Regex) https://automatetheboringstuff.com/2e/chapter7/
Chapter 8 - Input Validation https://automatetheboringstuff.com/2e/chapter8/