Isinstance
isinstance is a Python built-in function that tests whether an object is an instance of a specified class or tuple of classes, including subclasses.
The Quick Python Book, Fourth Edition
isinstance is a Python built-in function that tests whether an object is an instance of a specified class or tuple of classes.
- How it is used
- Uses inheritance-aware checks to validate expected types in methods and type-restricted containers.
- How deep it goes
- Explains inherited-instance behavior and works through container validation, without examining the built-in’s implementation.
- Examples
- Demonstrates subclass checks, a string-only dictionary, and a typed list whose allowed element type comes from an example value.
- What you can do after
- Apply it via Python’s built-in `isinstance` to reject unsuitable inputs or container elements with `TypeError`.
Read how The Quick Python Book, Fourth Edition explains isinstance →
Python How-To
isinstance is a Python built-in function that tests whether an object is an instance of a specified class or tuple of classes, including subclasses.
- How it is used
- Selects flexible runtime type checks for functions that accept related classes, multiple alternatives, or shared interfaces.
- How deep it goes
- Explains single-class, tuple, inheritance-aware, and abstract-class checks through focused function examples.
- Examples
- Uses integer and list assertions, list-or-tuple arguments, task filtering, and User–Supervisor inheritance comparisons.
- What you can do after
- Apply isinstance to build runtime checks that tolerate subclasses, alternative classes, and collection-like inputs.
Related concepts
- inheritanceuses · Inheritance is a mechanism by which a child type or element receives properties, values, or behavior from a parent, subject to system rules and possible overrides.
- type checkinguses · Type checking is the process of determining whether values, expressions, or operations conform to the rules or constraints of a type system.
- type functioncontrasts with · Python’s type() function returns an object’s type when called with one argument and can create a class when called with class-construction arguments.
- built-in functionkind of · A built-in function is a predefined callable operation supplied by a programming language, runtime, library, or execution environment.
- __setitem__used by · __setitem__ is a Python special method that defines how an object responds when an item or slice is assigned with subscription syntax.
- data typeuses · A data type is a classification that specifies the values data can represent, how they are represented or interpreted, and which operations apply to them.
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