Problem: What is the best way to check whether a given object is of a given type? For example, if you have a variable
object, how to check if it’s a
Check with Subclasses
Solution: To check if an
object is an instance of
str or any of its subclasses, use
if isinstance(o, str): print(o, 'is of type string')
Note that if the object inherits from string, the result of
isinstance(o, str) will also be
Here’s an example:
class Car: def speed(self): return 100 class Sportscar(Car): def speed(self): return 200 vw = Car() porsche = Sportscar() print(isinstance(vw, Car)) # True print(isinstance(porsche, Sportscar)) # True print(isinstance(porsche, Car)) # True --> Inherit being a Car from being a Sportscar
The example shows that the
vw is a
Car and the
porsche is a
Sportscar. However, as a
Sportscar inherits from
porsche is also a
However, you could argue that checking for type shouldn’t include checking for subclasses. So, in this example, the
porsche instance should not be a
Car. Let’s have a look how to accomplish this next!
Check without Subclasses
obj = 'hello' if type(obj) is str: print(obj, 'is of type string (it is not a subclass)')
The output is:
hello is of type string (it is not a subclass)
Similarly, if you use the same class example as before, the
porsche would now not be a
Car—even though it’s a
class Car: def speed(self): return 100 class Sportscar(Car): def speed(self): return 200 vw = Car() porsche = Sportscar() print(type(vw) is Car) # True print(type(porsche) is Sportscar) # True print(type(porsche) is Car) # False --> Inherit being a Car from being a Sportscar but is not of type Car
Resources: You may also enjoy to check out the following resources about Python typing:
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