monkeypatch.delattr in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output after monkeypatch.delattr removes an attribute?

Consider the following code using pytest's monkeypatch.delattr. What will be the output of the test function?

PyTest

class MyClass:
    def method(self):
        return "original"

def test_method(monkeypatch):
    obj = MyClass()
    monkeypatch.delattr(obj, "method")
    try:
        result = obj.method()
    except AttributeError:
        result = "AttributeError"
    print(result)

A AttributeError

B original

C TypeError

D None

💡 Hint

Think about what happens when you remove an attribute and then try to access it.

The monkeypatch.delattr removes the 'method' attribute from the instance 'obj'. When calling obj.method(), Python cannot find the method and raises AttributeError.

❓ assertion

intermediate

Which assertion correctly verifies that monkeypatch.delattr removed an attribute?

Given an object 'obj' with attribute 'attr', and after monkeypatch.delattr(obj, 'attr'), which assertion correctly checks that 'attr' is removed?

A assert obj.attr == ''

B assert hasattr(obj, 'attr') is False

C assert obj.attr is None

D assert hasattr(obj, 'attr') is True

💡 Hint

Use hasattr to check if an attribute exists.

After monkeypatch.delattr removes 'attr', hasattr(obj, 'attr') returns False. So asserting it is False confirms removal.

🔧 Debug

advanced

Why does monkeypatch.delattr fail to remove a class attribute when called on an instance?

Given this code: class MyClass: attr = 5 obj = MyClass() monkeypatch.delattr(obj, 'attr') Why does obj.attr still return 5 after delattr?

A Because monkeypatch.delattr cannot remove attributes from any object

B Because delattr requires the attribute name as bytes, not string

C Because attr is a private attribute and cannot be removed

D Because delattr on instance only removes instance attributes, not class attributes

💡 Hint

Think about where the attribute is stored: instance or class?

Attributes defined on the class are not stored on the instance. monkeypatch.delattr called on the instance removes only instance attributes, so class attributes remain accessible.

❓ framework

advanced

How does monkeypatch.delattr behave with the 'raising' parameter set to False?

What happens when you call monkeypatch.delattr(obj, 'missing_attr', raising=False) if 'missing_attr' does not exist on obj?

A It silently does nothing without raising an error

B It raises AttributeError immediately

C It removes all attributes from obj

D It creates 'missing_attr' with value None

💡 Hint

Check the effect of the 'raising' flag in monkeypatch.delattr.

With raising=False, monkeypatch.delattr does not raise an error if the attribute does not exist; it silently skips removal.

🧠 Conceptual

expert

What is the main advantage of using monkeypatch.delattr in tests?

Why would a tester prefer monkeypatch.delattr over manually deleting attributes in test setup?

A It improves test performance by caching attributes

B It permanently deletes the attribute from the class or instance

C It automatically restores the attribute after the test ends

D It converts attributes to private to prevent access

💡 Hint

Think about test isolation and cleanup.

monkeypatch.delattr removes attributes temporarily during a test and restores them after, ensuring tests do not affect each other.

Practice

1. What is the main purpose of monkeypatch.delattr in pytest?

easy

A. To temporarily remove an attribute from an object during a test

B. To permanently delete a file during testing

C. To add a new attribute to an object during a test

D. To reset all attributes of an object to default values

Solution

1. Step 1: Understand monkeypatch.delattr functionality

   It temporarily removes an attribute from an object only during the test execution.

2. Step 2: Compare with other options

   Options B, C, and D describe different actions unrelated to temporary attribute removal.

3. Final Answer:

   To temporarily remove an attribute from an object during a test -> Option A

4. Quick Check:

   monkeypatch.delattr = temporary attribute removal [OK]

Hint: Remember: delattr means deleting attribute temporarily [OK]

Common Mistakes:

• Confusing delattr with adding attributes
• Thinking it deletes files or permanent changes
• Assuming it resets attributes instead of removing

2. Which of the following is the correct syntax to remove the attribute foo from object obj using monkeypatch in pytest?

easy

A. monkeypatch.delattr('foo', obj)

B. monkeypatch.delattr(obj.foo)

C. monkeypatch.delattr('obj', foo)

D. monkeypatch.delattr(obj, 'foo')

Solution

1. Step 1: Recall monkeypatch.delattr syntax

   The correct syntax requires the object and the attribute name as a string: monkeypatch.delattr(object, 'attribute_name').

2. Step 2: Analyze options

   monkeypatch.delattr(obj, 'foo') matches the correct syntax. Options A, C, and D misuse argument order or types.

3. Final Answer:

   monkeypatch.delattr(obj, 'foo') -> Option D

4. Quick Check:

   delattr(object, 'attr') syntax = monkeypatch.delattr(obj, 'foo') [OK]

Hint: Use object first, then attribute name as string [OK]

Common Mistakes:

• Passing attribute without quotes
• Swapping object and attribute order
• Passing attribute as variable instead of string

3. Given the code below, what will happen when test_func runs?

class MyClass:
    def greet(self):
        return 'Hello'

def test_func(monkeypatch):
    obj = MyClass()
    monkeypatch.delattr(obj, 'greet')
    try:
        obj.greet()
    except AttributeError:
        print('Attribute missing')

medium

A. Prints 'Hello'

B. Does nothing and passes silently

C. Raises AttributeError and prints 'Attribute missing'

D. Raises TypeError

Solution

1. Step 1: Understand monkeypatch.delattr effect

   It removes the 'greet' method from obj temporarily during the test.

2. Step 2: Analyze the try-except block

   Calling obj.greet() after removal raises AttributeError, caught and prints 'Attribute missing'.

3. Final Answer:

   Raises AttributeError and prints 'Attribute missing' -> Option C

4. Quick Check:

   Removed attribute causes AttributeError caught and message printed [OK]

Hint: Removed method causes AttributeError when called [OK]

Common Mistakes:

• Expecting original method to run after deletion
• Confusing AttributeError with TypeError
• Ignoring exception handling block

4. You wrote this test code but it raises an error:

def test_example(monkeypatch):
    class Sample:
        def method(self):
            return 42
    obj = Sample()
    monkeypatch.delattr('obj', 'method')
    obj.method()

What is the error and how to fix it?

medium

A. Error: SyntaxError; fix by adding parentheses to method call

B. Error: AttributeError; fix by changing 'obj' to obj in delattr

C. Error: TypeError; fix by removing quotes around 'method'

D. Error: NameError; fix by defining obj before delattr

Solution

1. Step 1: Identify incorrect delattr usage

   Passing 'obj' as a string instead of the object causes AttributeError because monkeypatch expects the object itself.

2. Step 2: Correct the argument

   Change monkeypatch.delattr('obj', 'method') to monkeypatch.delattr(obj, 'method') to pass the actual object.

3. Final Answer:

   Error: AttributeError; fix by changing 'obj' to obj in delattr -> Option B

4. Quick Check:

   Pass object, not string, to delattr [OK]

Hint: Pass object, not string, as first argument [OK]

Common Mistakes:

• Passing object name as string instead of object
• Misplacing quotes around attribute name
• Ignoring error message details

5. You want to test how your code behaves when a method calculate is missing from an object calculator. Which pytest monkeypatch.delattr usage correctly simulates this scenario and allows you to assert the error handling?

hard

A. monkeypatch.delattr(calculator, 'calculate') before calling the method and assert AttributeError

B. monkeypatch.delattr(calculator, 'calculate') after calling the method to check result

C. monkeypatch.setattr(calculator, 'calculate', lambda: 0) to replace method

D. monkeypatch.delattr('calculator', 'calculate') to remove method

Solution

1. Step 1: Understand test goal

   You want to simulate the absence of 'calculate' method to test error handling.

2. Step 2: Apply monkeypatch.delattr correctly

   Removing 'calculate' before calling it triggers AttributeError, which you can assert. monkeypatch.delattr(calculator, 'calculate') before calling the method and assert AttributeError does this correctly.

3. Step 3: Analyze other options

   monkeypatch.delattr(calculator, 'calculate') after calling the method to check result removes method after call (too late). monkeypatch.setattr(calculator, 'calculate', lambda: 0) to replace method replaces method, not removes. monkeypatch.delattr('calculator', 'calculate') to remove method passes object name as string (incorrect).

4. Final Answer:

   monkeypatch.delattr(calculator, 'calculate') before calling the method and assert AttributeError -> Option A

5. Quick Check:

   Remove method before call to test missing attribute [OK]

Hint: Remove attribute before call to test missing method [OK]

Common Mistakes:

• Removing attribute after method call
• Replacing method instead of removing
• Passing object name as string instead of object