Repeated logic may run correctly, but it makes maintenance harder: every improvement or bug fix must be found and applied in several places. DRY means defining knowledge or behavior once, then reusing it. section 6.0 section 8.0
Prefer the compact condition
A repeated vowel comparison such as `if (word[0] == 'a' or word[0] == 'e' or word[0] == 'i' or word[0] == 'o' or word[0] == 'u'):` can become the clearer `if word[0] in 'aeiou':`. The shorter expression is readable, accurate, and uses Python's sequence membership operation. section 2.3
Choose the reuse boundary that matches where repetition occurs:
- Use a function when identical instructions recur within one program. A named function packages behavior, supports repeated calls, and lets the rest of the program operate at a higher level of abstraction. section 6.0
- Use a module when the same functions, classes, or data must be shared across programs. Importing the definition avoids reimplementing it and reduces the cognitive load of its implementation details. section 8.0 section 8.11
- Use inheritance when related classes share behavior. A subclass reuses its parent’s functionality and adds more specific behavior, although initialization must be designed so shared attributes are set correctly. section 9.15
Python functions add flexibility because they are objects: code can store them in data structures and retrieve them as data. This can reduce code while preserving reusable, named operations. section 6.0
