条件语句：if、elif、else

Conditionals let you run different code based on the value of a boolean expression. In Python they are written with if, elif (shorthand for "else if") and else.

The basic form

eta = 18
if eta >= 18:
    messaggio = "maggiorenne"
else:
    messaggio = "minorenne"

Notice:

• after the condition there's always a colon :;
• the block "inside" the if is identified by indentation (4 spaces);
• you don't need parentheses around the condition (although they are allowed).

More branches with elif

voto = 7
if voto >= 9:
    giudizio = "ottimo"
elif voto >= 7:
    giudizio = "buono"
elif voto >= 6:
    giudizio = "sufficiente"
else:
    giudizio = "insufficiente"

The elif branches are evaluated in the order you write them and they stop at the first one that turns out to be true.

Conditional expression (ternary)

For simple cases you can write everything on one line:

eta = 20
messaggio = "maggiorenne" if eta >= 18 else "minorenne"

It reads naturally in English: "maggiorenne if eta >= 18 else minorenne".

"Truthy" / "falsy" values

A condition doesn't have to be a comparison: any value can be used as a condition. These are considered false: False, None, 0, "", [], {}. Everything else is true.

nome = "Ada"
if nome:
    saluto = f"Ciao {nome}!"
else:
    saluto = "Ciao sconosciuto!"

Conditional expressions (ternary operator)

Python supports a compact single-line if-else construct, which acts as the ternary operator found in other languages:

result = "Even" if n % 2 == 0 else "Odd"

This keeps your code concise when you simply need to assign a value based on a condition.

Try it yourself

Review exercise

Additional challenge