Operators

Operators are the symbols that combine values to produce new ones. Python shares most operators with other languages, but introduces some very useful ones of its own.

Arithmetic operators

3 + 2     # 5      somma
3 - 2     # 1      differenza
3 * 2     # 6      prodotto
7 / 2     # 3.5    divisione (restituisce SEMPRE float)
7 // 2    # 3      divisione intera (tronca verso il basso)
7 % 2     # 1      resto (modulo)
2 ** 10   # 1024   potenza

Comparison operators

They return a bool (True or False):

3 == 3        # True   uguaglianza
3 != 4        # True   diversità
3 < 4         # True   minore
3 <= 3        # True   minore o uguale
"a" < "b"     # True   confronto lessicografico

Unlike JavaScript, in Python there is only one equality operator (==): no need to choose between == and ===.

Logical operators

They are written with English words, not symbols:

True and False    # False
True or False     # True
not True          # False

They also have a very useful short-circuit behavior: a and b returns a if it's "falsy", otherwise b.

What counts as "falsy"

In Python, these are considered false: False, None, 0, 0.0, the empty string "", the empty list [], the empty dict {}. Everything else is considered true.

Priority in brief

To memorize: ** → * / // % → + - → comparisons → not → and → or. When in doubt, use parentheses: they cost nothing and make the code more readable.

Floor division and rounding

The floor division operator // always truncates the result down to the next integer. This means that for positive numbers 7 // 2 yields 3, but for negative numbers -7 // 2 yields -4. The modulo operator % calculates the remainder of integer division and is widely used to determine whether a number is a multiple of another (e.g. n % 2 == 0 checks if n is even).

Try it yourself

Review exercise

Additional challenge