BeginnerCore syntax

Variables and types

Names point at values. Values have types. Get this right and Python stays predictable.

PythonBeginner8 min read

By the end of this lesson you will be able to:

Explain what a Python variable actually is (a name bound to a value)
Identify the core built-in types and when to use each
Predict the result of mixing types, and read a TypeError

In Python, a variable is a name bound to a value. The name is just a label; the value is the real thing, sitting in memory. Assignment points the label at a value:

message = "hello"
count = 3
count = count + 1   # rebinds `count` to the value 4

message doesn't contain the text — it refers to it. This matters the moment two names refer to the same object, which you'll meet soon with lists.

The core built-in types

Every value has a type that determines what it is and what you can do with it. The ones you'll use constantly:

int — whole numbers: 42, -7
float — numbers with a decimal point: 3.14, 2.0
str — text, in quotes: "hello", 'world'
bool — True or False
list — an ordered, changeable collection: [1, 2, 3]
dict — key→value pairs: {"name": "Ada", "born": 1815}
None — the deliberate absence of a value

You can always ask what something is:

type(3)        # <class 'int'>
type(3.0)      # <class 'float'>
type("3")      # <class 'str'>

Dynamic typing, with consequences

Python is dynamically typed: a name can be bound to a value of any type, and the type travels with the value, not the name. This is flexible, but it means Python checks types as it runs, not before:

"price: " + 10        # TypeError: can only concatenate str (not "int") to str
"price: " + str(10)   # "price: 10"  ✓ convert first

That error is Python telling you it won't guess what you meant by "add a number to some text." You have to convert explicitly — turn the int into a str with str(...), or the str into an int with int(...).

Try it yourself — this runs real Python in your browser. Edit it, break it, fix it:

Python — editable, runs in your browser

int and float mix freely (1 + 2.0 is 3.0), because Python knows how to promote an int to a float. It just refuses to silently guess across less obvious boundaries like str and int — exactly the kind of ambiguity that hides bugs.

Truthiness

In a boolean context, every value is either "truthy" or "falsy." Empty things are falsy:

bool(0)        # False
bool("")       # False
bool([])       # False
bool(None)     # False
bool(42)       # True
bool("hi")     # True

This is why if my_list: reads naturally as "if the list has anything in it."

Check your understanding

Knowledge check

Where to go next

Next: control flow — using these values to make decisions and repeat work with if, for, and while.

Finished reading? Mark it complete to track your progress.

Python

Syntax and idioms for a famously readable language.

Control flow

Make decisions with if, repeat with for and while — and meet Python's significant whitespace.