{"id":421,"date":"2024-01-29T11:06:25","date_gmt":"2024-01-29T11:06:25","guid":{"rendered":"https:\/\/learnpython.elegantwallp.com\/?p=421"},"modified":"2024-01-29T11:06:26","modified_gmt":"2024-01-29T11:06:26","slug":"python-assertisinstance","status":"publish","type":"post","link":"https:\/\/learnpython.elegantwallp.com\/2024\/01\/29\/python-assertisinstance\/","title":{"rendered":"Python assertIsInstance()"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you\u2019ll learn how to use Python assertIsInstance()<\/code> method to test if an object is an instance of a class.<\/p>\n\n\n\n

Introduction to the Python assertIsInstance() method<\/h2>\n\n\n\n

The\u00a0assertIsInstance()<\/code>\u00a0is a method of the\u00a0TestCase<\/code>\u00a0class of the\u00a0unittest\u00a0module. The\u00a0assertIsInstance()<\/code>\u00a0method tests if an object is an instance of a\u00a0class.<\/p>\n\n\n\n

The following shows the syntax of the\u00a0assertIsInstance()<\/code>\u00a0method:<\/p>\n\n\n\n

assertIsInstance(obj, cls, msg=None)<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
In this syntax:<\/p>\n\n\n\n
    \n
  • obj<\/code> is the object to test.<\/li>\n\n\n\n
  • cls<\/code>\u00a0is a class or a\u00a0tuple\u00a0of classes.<\/li>\n\n\n\n
  • msg<\/code> is an optional string that will be displayed if the obj<\/code> is not an instance of the cls<\/code> class.<\/li>\n<\/ul>\n\n\n\n
    Internally, the assertIsInstance()<\/code> uses the isinstance()<\/code> function to check if the object is an instance of the cls<\/code> class.<\/p>\n\n\n\n
    If the cls<\/code> is not the class of the obj but the base class of the class of the obj, the test will also pass.<\/p>\n\n\n\n
    Since the object class is the base class of all classes, the assertIsInstance(obj, object)<\/code> will always pass.<\/p>\n\n\n\n
    Python assertIsInstance() method examples<\/h2>\n\n\n\n
    Let\u2019s create a\u00a0shape.py<\/code>\u00a0module with two classes\u00a0Shape<\/code>\u00a0and\u00a0Square<\/code>. The\u00a0Shape<\/code>\u00a0class is the base class of the\u00a0Square<\/code>\u00a0class:<\/p>\n\n\n\n
    class Shape: pass class Square(Shape): pass<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    To make it simple, the Shape<\/code> and Square<\/code> classes have no implementation.<\/p>\n\n\n\n
    1) Using the Python assertIsInstance() method example<\/h3>\n\n\n\n
    The following example uses the\u00a0assertIsInstance()<\/code>\u00a0method to test if the\u00a0square<\/code>\u00a0object is an instance of the\u00a0Square<\/code>\u00a0class:<\/p>\n\n\n\n
    import unittest from shape import Shape, Square class TestShape(unittest.TestCase): def setUp(self): self.square = Square() def test_is_instance(self): self.assertIsInstance(self.square, Square)<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    Run the test:<\/p>\n\n\n\n
    python -m unittest -v<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    Output:<\/p>\n\n\n\n
    test_is_instance (test_shape.TestShape) ... ok ---------------------------------------------------------------------- Ran 1 test in 0.001s OK<\/code>Code language: plaintext (plaintext)<\/small><\/code><\/pre>\n\n\n\n
    Because the square<\/code> instance variable is an object of the Square<\/code> class, the test passes.<\/p>\n\n\n\n
    2) Using the Python assertIsInstance() method with a base class example<\/h3>\n\n\n\n
    The following example uses the\u00a0assertIsInstance()<\/code>\u00a0method to test if the\u00a0square<\/code>\u00a0is an instance of the\u00a0Shape<\/code>\u00a0class:<\/p>\n\n\n\n
    import unittest from shape import Shape, Square class TestShape(unittest.TestCase): def setUp(self): self.square = Square() def test_is_instance(self): self.assertIsInstance(self.square, Square) def test_is_instance_of_parent_class(self): self.assertIsInstance(self.square, Shape)<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    Run the test:<\/p>\n\n\n\n
    python -m unittest -v<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    Output:<\/p>\n\n\n\n
    test_is_instance (test_shape.TestShape) ... ok test_is_instance_of_parent_class (test_shape.TestShape) ... ok ---------------------------------------------------------------------- Ran 2 tests in 0.001s OK<\/code>Code language: plaintext (plaintext)<\/small><\/code><\/pre>\n\n\n\n
    3) Using the Python assertIsInstance() method to test if an object is an instance of the object class<\/h3>\n\n\n\n
    The following example uses\u00a0assertIsInstance()<\/code>\u00a0method to test if the\u00a0square<\/code>\u00a0instance variable is an instance of the\u00a0object<\/code>\u00a0class:<\/p>\n\n\n\n
    import unittest from shape import Shape, Square class TestShape(unittest.TestCase): def setUp(self): self.square = Square() def test_is_instance(self): self.assertIsInstance(self.square, Square) def test_is_instance_of_parent_class(self): self.assertIsInstance(self.square, Shape) def test_is_instance_of_object(self): self.assertIsInstance(self.square, object)<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    Run the test:<\/p>\n\n\n\n
    python -m unittest -v<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    Output:<\/p>\n\n\n\n
    test_is_instance (test_shape.TestShape) ... ok test_is_instance_of_object (test_shape.TestShape) ... ok test_is_instance_of_parent_class (test_shape.TestShape) ... ok ---------------------------------------------------------------------- Ran 3 tests in 0.001s OK<\/code>Code language: plaintext (plaintext)<\/small><\/code><\/pre>\n\n\n\n
    Python assertIsNotInstance() method<\/h2>\n\n\n\n
    The\u00a0assertIsNotInstance()<\/code>\u00a0is the opposite of the\u00a0assertIsInstance()<\/code>\u00a0method. It tests if an object is not an instance of a class:<\/p>\n\n\n\n
    assertNotIsInstance(obj, cls, msg=None)<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    For example:<\/p>\n\n\n\n
    import unittest from shape import Shape, Square class TestShape(unittest.TestCase): def setUp(self): self.square = Square() def test_is_instance(self): self.assertIsInstance(self.square, Square) def test_is_instance_of_parent_class(self): self.assertIsInstance(self.square, Shape) def test_is_instance_of_object(self): self.assertIsInstance(self.square, object) def test_is_not_instance(self): shape = Shape() self.assertNotIsInstance(shape, Square)<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    In this example, the test_is_not_instance()<\/code> method uses the assertIsNotInstance()<\/code> method to test if a Shape<\/code> object is an instance of the Square<\/code> class.<\/p>\n\n\n\n
    Run the test:<\/p>\n\n\n\n
    python -m unittest -v<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    Output:<\/p>\n\n\n\n
    test_is_instance (test_shape.TestShape) ... ok test_is_instance_of_object (test_shape.TestShape) ... ok test_is_instance_of_parent_class (test_shape.TestShape) ... ok test_is_not_instance (test_shape.TestShape) ... ok ---------------------------------------------------------------------- Ran 4 tests in 0.002s OK<\/code><\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"
    Summary: in this tutorial, you\u2019ll learn how to use Python assertIsInstance() method to test if an object is an instance of a class. Introduction to the Python assertIsInstance() method The\u00a0assertIsInstance()\u00a0is a method of the\u00a0TestCase\u00a0class of the\u00a0unittest\u00a0module. The\u00a0assertIsInstance()\u00a0method tests if an object is an instance of a\u00a0class. The following shows the syntax of the\u00a0assertIsInstance()\u00a0method: In this syntax: Internally, […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[43],"tags":[],"class_list":["post-421","post","type-post","status-publish","format-standard","hentry","category-3-python-unit-testing"],"_links":{"self":[{"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/posts\/421","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/comments?post=421"}],"version-history":[{"count":1,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/posts\/421\/revisions"}],"predecessor-version":[{"id":422,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/posts\/421\/revisions\/422"}],"wp:attachment":[{"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/media?parent=421"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/categories?post=421"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/tags?post=421"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}