7 Python One-Liners That Replace 20 Lines of Code

Every Python developer has that moment — you write a clean 15-line function, then a colleague rewrites it in one line that does the same thing. These are not code golf tricks. These are real patterns I use daily that make code shorter and more readable. 1. Dictionary Merge (Replace 5 Lines) Before: result = {} for key in defaults : result [ key ] = defaults [ key ] for key in overrides : result [ key ] = overrides [ key ] After: result = { ** defaults , ** overrides } # Python 3.5+ # Or even cleaner in 3.9+: result = defaults | overrides 💡 The | operator also works with |= for in-place merge. 2. Conditional List Building (Replace 8 Lines) Before: result = [] for item in data : if item . is_active : transformed = item . name . upper () if transformed not in seen : seen . add ( transformed ) result . append ( transformed ) After: result = list ( dict . fromkeys ( item . name . upper () for item in data if item . is_active )) 💡 dict.fromkeys() preserves insertion order while deduplicating