Deck 6: Conditionals

What does this print if expression = 4.2 and threshold = 2.0?
if expression > threshold:

print('Gene is upregulated')

else:

print('Gene expression is normal')

"Gene is upregulated" (4.2 > 2.0 is True)

Why use if/else instead of two separate if statements checking opposite conditions?

if/else guarantees exactly one branch runs, making the "exactly one of these happens" relationship explicit and safe from accidental edits later

In an if/elif/elif/else chain, which condition wins if multiple are true?

The first one that's true, checked top to bottom → the rest are skipped even if they'd also be true

Why does condition order matter in an elif chain (e.g. checking > 5 before > 2)?

If a broader condition (> 2) came first, it would catch values that should have matched a more specific condition (> 5), so the more specific condition never gets reached — put the most specific condition first.

What do and, or, and not do in a conditional?

and requires both sides true; or requires at least one side true; not flips true to false or false to true.

How does pandas' condition-combining syntax differ from plain Python's and/or?

pandas uses & and | instead of and/or when combining conditions across whole DataFrame columns.