Checking identity (is, is not) in PyTest - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the is operator check in Python?

The is operator checks if two variables point to the exact same object in memory, not just if they have the same value.

beginner

How is is not different from != in Python?

is not checks if two variables are not the same object (different identity), while != checks if their values are different.

beginner

In pytest, how do you assert that two variables are the same object?

Use assert a is b to check that a and b refer to the same object in memory.

intermediate

Why might is be preferred over == in some tests?

Because is confirms the exact object identity, which is important when you want to ensure no copies or different instances are involved.

beginner

What will this pytest assertion check? <br>

assert a is not b

It checks that a and b are not the same object in memory. They can have the same value but must be different objects.

What does assert a is b verify in pytest?

A That a and b are the same object

B That a and b are different objects

C That a and b have the same value

D That a and b are both None

is checks object identity, so the assertion verifies a and b refer to the same object.

Which operator checks if two variables do NOT refer to the same object?

A is

B is not

C !=

D ==

is not checks that two variables are not the same object in memory.

If a == b is True but a is b is False, what does it mean?

A a and b are the same object

B a and b have different values

C a and b have the same value but are different objects

D a or b is None

Equality means same value, but identity means same object. Here, values match but objects differ.

Which pytest assertion checks that two variables are NOT the same object?

A assert a is not b

B assert a != b

C assert a == b

D assert a is b

assert a is not b confirms a and b are different objects.

Why is using is important when testing singleton objects like None?

A Because <code>is</code> checks value equality

B Because <code>is</code> compares types

C Because <code>is</code> converts objects to strings

D Because <code>is</code> checks object identity, ensuring the singleton is used

Singletons like None have only one instance, so is confirms the exact object is used.

Explain the difference between is and == in Python testing.

Think about whether you want to check if two things are exactly the same object or just look the same.

Describe how to write a pytest assertion to verify two variables are not the same object.

Focus on the keyword that means 'not the same object'.