Tutorial

2. Values and types

The basic types#

age: int = 36
height: float = 1.82
name: str = "Ada"
active: bool = True
print(age, height, name, active)

36 1.82 Ada True

A variable is created by its first assignment, which carries the type. Later assignments do not repeat it:

counter: int = 0
counter = counter + 1
counter += 1
print(counter)

2

Assigning a value of the wrong type is a compile error — counter = "one" would be rejected before the program runs.

Arithmetic#

print(7 + 2, 7 - 2, 7 * 2, 7 / 2, 7 // 2, 7 % 2, 7 ** 2)
print(-7 // 2, -7 % 2)

9 5 14 3.5 3 1 49
-4 1

/ always gives a float; // and % round toward minus infinity, like Python. Mixing an int and a float gives a float.

Strings#

first: str = "Ada"
last: str = "Lovelace"
full: str = first + " " + last
print(full, len(full), full.upper(), full[0], full[-1])
print(full.split(" "), "Love" in full, full.replace("a", "4"))

Ada Lovelace 12 ADA LOVELACE A e
['Ada', 'Lovelace'] True Ad4 Lovel4ce

Strings are immutable and indexed by character (code point), so non-English text works as you expect.

f-strings#

Put an expression in braces inside an f"..." string. A format specification after a colon controls the layout:

item: str = "tea"
price: float = 3.5
qty: int = 4
print(f"{item}: {qty} x {price} = {qty * price}")
print(f"{price:8.2f}|{qty:03d}|{item:>6}|{1234567:,}")

tea: 4 x 3.5 = 14.0
    3.50|004|   tea|1,234,567

Converting between types#

Conversions are always explicit:

print(int("42") + 1, float("2.5") * 2, str(7) + "!", int(3.9), float(3), bool(0))

43 5.0 7! 3 3.0 False

int("abc") raises ValueError (chapter 7). The only implicit conversion is int → float when a float is expected.

Reading input#

line: str = input()
print("you typed:", line)

input() reads one line from standard input.

Conditions are bools#

Nox does not treat 0, "" or [] as false. A condition must be a bool, produced by a comparison:

n: int = 0
if n == 0:
    print("zero")
items: list[int] = []
if len(items) == 0:
    print("empty")

zero
empty

Numbers that must not overflow#

int wraps around at 64 bits. For code that must never overflow silently there are fixed-width types such as u8 and i32 that stop the program instead — see Numbers.

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