type()

Learn dynamic class creation with type().

Dynamic classes with type()

With one argument type() returns an object's type. With three arguments it creates a new class: type(name, bases, dict).

Here name is the class name, bases is a tuple of parent classes and dict is the namespace of attributes and methods. The result works like a class written with class. This lets you build structure from data; for example you can generate classes from a settings file.

The dict argument

The third argument — the dict — defines the class namespace. Entries like "x": 0 become instance attributes, entries like "show": lambda self: ... become methods.

The first parameter of a method is self. You can also add __init__ to the dict; then the dynamic class gets a constructor. This flexibility lets you build at runtime anything you could write with a class statement.

Exercise Build the Point class with type()

Build the Point class with type(). The second argument is the empty tuple (), the third is a dict. The dict should have x and y attributes (value 0) and a show method. show returns f"{self.x},{self.y}". Create an instance, set x=3 and y=4, then print show().

Show example solution

# Build the Point class dynamically
Point = type("Point", (), {
    "x": 0,
    "y": 0,
    "show": lambda self: f"{self.x},{self.y}",
})
p = Point()
p.x = 3
p.y = 4
print(p.show())

Test yourself

What does type("X", (), {}) return?
```
cls = type("X", (), {})
```
- It raises an error
- An empty object
- A new class object
- The type object itself
Show answer

A new class object — type with three arguments creates and returns a new class.

Complete the type() call

Point = type("Point", (), {____, "y": 0})

Show answer

Point = type("Point", (), {"x": 0, "y": 0})

Match type() concepts

type

Creates a class
isim

Class name
tabanlar

Base class tuple
sözlük

Attribute map

Next lesson: Metaclass

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