Checking identity (is, is not) in PyTest - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if two variables refer to the same object using identity operator.

PyTest

def test_identity():
    a = [1, 2, 3]
    b = a
    assert a [1] b

Drag options to blanks, or click blank then click option'

Ais not

B==

Cis

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of 'is' for identity check.

The is operator checks if two variables point to the same object in memory.

2fill in blank

medium

Complete the code to assert two variables do NOT refer to the same object.

PyTest

def test_not_identity():
    a = [1, 2, 3]
    b = [1, 2, 3]
    assert a [1] b

Drag options to blanks, or click blank then click option'

Ais

Bis not

C==

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of 'is not' for identity check.

The is not operator checks that two variables do not point to the same object.

3fill in blank

hard

Fix the error in the assertion to correctly check identity.

PyTest

def test_identity_error():
    a = None
    b = None
    assert a [1] b

Drag options to blanks, or click blank then click option'

Ais

Bis not

C!=

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of 'is' to compare with None.

Use is to check if both variables point to the same None object.

4fill in blank

hard

Fill both blanks to create a test that asserts two variables are not the same object and have equal content.

PyTest

def test_not_same_but_equal():
    a = [1, 2]
    b = [1, 2]
    assert a [1] b
    assert a [2] b

Drag options to blanks, or click blank then click option'

A==

Bis

Cis not

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up 'is' and '==' operators.

The first assertion checks equality of content with ==, the second checks that they are different objects with is not.

5fill in blank

hard

Fill all three blanks to complete the test checking identity and inequality correctly.

PyTest

def test_identity_and_equality():
    x = 'hello'
    y = ''.join(['h', 'e', 'l', 'l', 'o'])
    assert x [1] y
    assert x [2] y
    assert x [3] y

Drag options to blanks, or click blank then click option'

A!=

B==

Cis not

Dis

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing identity and equality operators.

x and y have the same content but are different objects. So is not is true, == is true, and != is false.

Practice

1. What does the is operator check in Python when used in pytest assertions?

easy

A. If two variables have the same value but different objects

B. If two variables point to the exact same object in memory

C. If two variables are equal using the == operator

D. If two variables are both integers

Solution

1. Step 1: Understand the is operator meaning

   The is operator checks if two variables refer to the same object in memory, not just equal values.

2. Step 2: Differentiate from ==

   The == operator checks if values are equal, but is checks identity (same object).

3. Final Answer:

   If two variables point to the exact same object in memory -> Option B

4. Quick Check:

   is checks identity [OK]

Hint: Remember: is means same object, not just equal value [OK]

Common Mistakes:

• Confusing is with ==
• Thinking is checks value equality
• Using is for comparing numbers or strings incorrectly

2. Which of the following is the correct syntax to assert two variables a and b are not the same object in pytest?

easy

A. assert a is not b

B. assert a !== b

C. assert a is! b

D. assert a != b

Solution

1. Step 1: Recall correct syntax for identity negation

   The correct syntax to check two variables are not the same object is is not, so assert a is not b.

2. Step 2: Identify invalid syntax options

   Options B and C use invalid Python syntax. assert a != b uses != which checks value inequality, not identity.

3. Final Answer:

   assert a is not b -> Option A

4. Quick Check:

   is not syntax correct [OK]

Hint: Use is not to check different objects, not != [OK]

Common Mistakes:

• Using != instead of is not
• Writing is! which is invalid
• Using JavaScript style !== in Python

3. Given the code:

obj1 = None
obj2 = None

assert obj1 is obj2

What will happen when this pytest assertion runs?

medium

A. SyntaxError due to wrong assertion

B. The assertion fails because None is not an object

C. The assertion passes because both are the same None object

D. The assertion fails because obj1 and obj2 are different None instances

Solution

1. Step 1: Understand None is a singleton

   In Python, None is a singleton object, so all variables assigned None point to the same object.

2. Step 2: Check identity assertion

   The assertion assert obj1 is obj2 checks if both variables point to the same object, which they do.

3. Final Answer:

   The assertion passes because both are the same None object -> Option C

4. Quick Check:

   None is None always True [OK]

Hint: Remember: None is always the same object in Python [OK]

Common Mistakes:

• Thinking None creates new objects each time
• Confusing identity with equality
• Expecting assertion failure for None identity

4. Identify the error in this pytest assertion:

list1 = [1, 2, 3]
list2 = [1, 2, 3]
assert list1 is list2

medium

A. RuntimeError because lists cannot be compared with is

B. No error; assertion passes because lists have same values

C. SyntaxError due to wrong use of is

D. Assertion fails because lists are different objects despite same values

Solution

1. Step 1: Understand list object identity

   Two lists with same values are different objects in memory unless explicitly assigned.

2. Step 2: Check assertion behavior

   The assertion assert list1 is list2 fails because is checks identity, not equality.

3. Final Answer:

   Assertion fails because lists are different objects despite same values -> Option D

4. Quick Check:

   Same values ≠ same object [OK]

Hint: Use == for value equality, is for identity [OK]

Common Mistakes:

• Expecting is to check value equality
• Confusing object identity with content equality
• Assuming lists with same content share identity

5. You want to write a pytest test to confirm that a function returns the exact same singleton object config every time it is called. Which assertion is best?

hard

A. assert get_config() is config

B. assert get_config() == config

C. assert get_config() is not config

D. assert get_config() != config

Solution

1. Step 1: Understand singleton identity check

   To confirm the function returns the exact same object, use is to check identity.

2. Step 2: Evaluate options

   assert get_config() == config checks value equality, which may be true for different objects. assert get_config() is config correctly asserts identity. Options C and D check for difference, which is not desired.

3. Final Answer:

   assert get_config() is config -> Option A

4. Quick Check:

   is for singleton identity [OK]

Hint: Use is to confirm same singleton object returned [OK]

Common Mistakes:

• Using == which checks value, not identity
• Using is not by mistake
• Not understanding singleton pattern in tests