Python Functions and Scope Questions and Answers

Question 1

A developer writes a function to log messages, intending for each call to start with a fresh list of tags unless specified. However, they notice that tags from previous calls are persisting. What is the most likely cause of this bug?

```python
def log_message(message, tags=[]):
    tags.append('INFO')
    print(f"{message}: {tags}")

log_message("System start")
log_message("User login")
```

Accepted Answer

A mutable object (a list) is used as a default argument, which is evaluated only once when the function is defined.

Answer

The `tags` list was not declared as a global variable.

Answer

The function is a closure, causing it to retain the state of `tags`.

Answer

The `append` method modifies the list in-place, which is not allowed for function parameters.

Question 2

In Python's scope resolution, what is the LEGB rule?

Accepted Answer

The sequence Python follows to find a variable: Local, Enclosing, Global, Built-in.

Answer

The order of operations for arithmetic expressions: Logarithm, Exponentiation, Globals, Brackets.

Answer

A rule for naming variables: Lowercase, Extended, Grouped, Brief.

Answer

A memory management principle: Least-used, Expired, Garbage-collected, Blocked.

Question 3

What is the primary purpose of the `nonlocal` keyword in Python?

Accepted Answer

To allow an inner function to modify a variable from its nearest enclosing (but non-global) scope.

Answer

To declare a variable that can be accessed from any module in the program.

Answer

To prevent a variable from being modified by any function.

Answer

To create a variable that exists only within a `for` or `while` loop.

Question 4

Consider the following code. What will be the output?

```python
def multiplier_factory(n):
    def multiplier(x):
        return x * n
    return multiplier

double = multiplier_factory(2)
triple = multiplier_factory(3)

print(double(5), triple(5))
```

Accepted Answer

10 15

Answer

10 10

Answer

An error because `n` is not defined in the `multiplier` scope.

Answer

2 3

Question 5

A programmer needs to modify a global variable from within a function. Which of the following code snippets correctly accomplishes this?

Accepted Answer

```python
count = 0
def increment():
    global count
    count += 1
```

Answer

```python
count = 0
def increment():
    count += 1
```

Answer

```python
count = 0
def increment(count):
    count += 1
    return count
```

Answer

```python
count = 0
def increment():
    nonlocal count
    count += 1
```

Question 6

Which of the following statements about function arguments in Python is true?

Accepted Answer

Python uses a mechanism called 'pass-by-object-reference' or 'pass-by-assignment', where the function gets a copy of the reference to the object.

Answer

All arguments are passed by value, meaning a copy of the object is passed to the function.

Answer

Arguments are passed by reference, and any modification to a parameter within a function will always affect the original object.

Answer

Positional arguments must always be specified after keyword arguments in a function call.