Chapter 1 · Curious Beginner

Variables and types

variables · typesFND-1022 of 84

A variable is a name that points at a value. You create one with name = value. The = is *assignment* — "make this name refer to this value" — not the maths equals.

Every value has a type. The four you meet first:

str — text, in quotes: "rungo-api"
int — whole numbers, no quotes: 1, -40, 9000
float — numbers with a decimal point: 3.14, 2.0
bool — truth values, the bare words True and False (capital T/F)

Python is *dynamically typed*: you don't declare the type, Python works it out from the value. A variable can even be reassigned to a different type later (though doing that casually is a smell). Use type(x) to ask what type a value is.

Syntax

name = value

service_name = "rungo-api"  # str
version = 1                  # int
ratio = 0.75                 # float
is_live = True               # bool

Worked examples

Storing three values of different types

service_name = "rungo-api"
version = 1
is_live = True

print(service_name, version, is_live)
# Output:
# rungo-api 1 True

Checking a value's type

print(type(1))       # <class 'int'>
print(type(1.0))     # <class 'float'>
print(type("1"))     # <class 'str'>
print(type(True))    # <class 'bool'>

Reassigning a variable (the name re-points)

count = 5
count = count + 1
print(count)  # 6

Common mistakes & gotchas

true / false are not booleans

Python's booleans are True and False with a capital first letter. Lowercase true is treated as a variable name and raises NameError.

"1" is not 1

The string "1" is text; the int 1 is a number. "1" + "1" gives "11" (joined text), while 1 + 1 gives 2. Mixing them — "1" + 1 — raises TypeError.

= versus ==

A single = assigns a value. Double == compares two values and gives a bool. x = 5 stores 5; x == 5 asks "is x equal to 5?". Using = where you meant == is a classic beginner bug.

Why it matters

Variables are how a program remembers things between steps. Knowing the type of a value tells you what you can do with it — you can add ints, join strings, and test bools — and most early errors come from a value being a different type than you assumed.