PCAP Practice Test 20 — 15 Questions

Question 1

Which of the following is the correct way to open a file for writing in binary mode?

Accepted Answer

open('data.dat', 'wb'). The mode string 'wb' specifies both write ('w') and binary ('b') mode, which is the proper way to open a file for writing binary data in Python. The order of characters in the mode string is fixed: the file mode character ('r', 'w', 'a', etc.) must come first, followed by the optional 'b' for binary mode.

Answer

open('data.dat', 'bw')

Answer

open('data.dat', 'br')

Answer

open('data.dat', 'w')

Question 2

When should you raise a specific exception class rather than a generic Exception?

Accepted Answer

When different error conditions require different handling.. Raising a specific exception class (e.g., ValueError, KeyError, or a custom subclass) allows the caller to catch and handle each error condition differently using separate except blocks. Using a generic Exception forces all errors into a single handler, which can mask distinct failure modes and make debugging harder. This aligns with Python's EAFP (Easier to Ask for Forgiveness than Permission) idiom, where precise exception types enable fine-grained error recovery.

Answer

Always raise Exception for simplicity.

Answer

Specific exceptions cannot be created; only built-in ones can be used.

Answer

Only when performance is a concern.

Question 3

A developer wants to ensure that the 'radius' attribute of a Circle class is always non-negative. Which implementation using @property is correct?

Accepted Answer

class Circle:
    def __init__(self, radius):
        self.radius = radius
    @property
    def radius(self):
        return self._radius
    @radius.setter
    def radius(self, value):
        if value < 0:
            raise ValueError
        self._radius = value. It uses the @property decorator to define a getter and @radius.setter to define a setter that validates the radius value before assignment. The __init__ method correctly assigns to self.radius, which triggers the setter, ensuring the initial value is also validated. This pattern enforces the invariant that radius is always non-negative.

Answer

class Circle:
    def __init__(self, radius):
        self._radius = radius
    def radius(self):
        return self._radius

Answer

class Circle:
    def __init__(self, radius):
        self._radius = radius
    @property
    def radius(self):
        return self._radius
    @radius.setter
    def radius(self, value):
        if value < 0:
            raise ValueError
        self._radius = value

Answer

class Circle:
    def __init__(self, radius):
        self.radius = radius
    @property
    def radius(self):
        return self._radius
    def set_radius(self, value):
        self._radius = value

Question 4

Refer to the exhibit. What is the output?

Accepted Answer

HI, WORLD!. The code uses the `upper()` method on the string `'Hi, World!'`, which converts all lowercase letters to uppercase. The output is `'HI, WORLD!'`. The `upper()` method does not modify the original string but returns a new string with all characters in uppercase.

Answer

Hi, World!

Answer

Hello, World!

Answer

HELLO, WORLD!

Question 5

A class 'Point' is defined with __slots__ = ['x', 'y']. A developer creates an instance p = Point() and tries to set p.z = 10. What happens?

Accepted Answer

AttributeError is raised. When a class defines `__slots__`, it restricts attribute assignment to only those names listed in the tuple. Attempting to assign an attribute not in `__slots__` raises an `AttributeError`. This is a deliberate memory optimization that prevents the creation of a per-instance `__dict__`, so dynamic attributes are disallowed.

Answer

The assignment is silently ignored

Answer

Python issues a warning and adds the attribute

Answer

The attribute 'z' is added dynamically

Question 6

Which TWO of the following are true about the 'with' statement in Python file I/O?

Accepted Answer

It is equivalent to a try/finally block. The 'with' statement in Python is designed to simplify exception handling by encapsulating the setup and teardown of a resource in a context manager, which is functionally equivalent to a try/finally block. When you use 'with', the context manager's __exit__ method is guaranteed to be called even if an exception occurs, ensuring that cleanup actions like closing a file are performed, just as a finally clause would.

Answer

It can only be used with file objects

Answer

It does not require an __exit__ method

Answer

It requires the object to have an __enter__ method only

Question 7

A developer wants to check if a string contains only alphabetic characters. Which string method should be used?

Accepted Answer

isalpha(). The `isalpha()` method returns `True` if all characters in the string are alphabetic (letters) and the string is non-empty. This directly matches the developer's requirement to check for only alphabetic characters.

Answer

isalnum()

Answer

isspace()

Answer

isdigit()

Question 8

A developer wants a class 'Point' to have a readable string representation that returns 'Point(x, y)'. Which special method should be overridden?

Accepted Answer

__repr__. The `__repr__` method is designed to return an unambiguous string representation of an object, often used for debugging and development. Overriding `__repr__` to return `'Point(x, y)'` fulfills the requirement for a readable string representation that matches the specified format. This method is called by the `repr()` built-in function and by the interactive interpreter when evaluating an expression.

Answer

__format__

Answer

__str__

Answer

__unicode__

Question 9

Given s = 'Python', which THREE of the following expressions evaluate to True? (Choose three.)

Accepted Answer

'th' in s. The `in` operator checks for substring membership, and 'th' is indeed a contiguous substring within the string 'Python'. Python's `in` operator performs a linear scan of the string to determine if the substring exists, returning True if found.

Answer

s[0] == 'p'

Answer

s.isupper()

Question 10

Which of the following correctly raises a new exception while preserving the original traceback?

Accepted Answer

raise ValueError('new') from original_exception. The `raise ... from original_exception` syntax in Python allows you to raise a new exception while chaining it to the original exception, preserving the original traceback. This is essential for debugging, as it shows both the new error and the root cause.

Answer

raise original_exception

Answer

raise ValueError('new')

Answer

raise

Question 11

Which three of the following statements about Python strings are true? (Choose three.)

Accepted Answer

The join() method is called on the separator string.. The join() method is called on the separator string, not on the iterable. For example, ','.join(['a', 'b']) returns 'a,b'. The separator is the string that will be placed between each element of the iterable passed as an argument. This is a common point of confusion because many learners mistakenly think join() is called on the list.

Answer

The string '123.45' can be converted to integer using int('123.45').

Answer

Strings are mutable.

Question 12

Given s = 'Python', what is s[1:4]?

Accepted Answer

'yth'. In Python, string slicing with `s[start:stop]` extracts characters from index `start` up to but not including index `stop`. Since indexing starts at 0, `s[1:4]` on 'Python' takes indices 1 ('y'), 2 ('t'), and 3 ('h'), resulting in 'yth'. Option B is correct because it exactly matches this slice.

Answer

'pyt'

Answer

'ytho'

Answer

'Pyt'

Question 13

A developer needs to replace all occurrences of 'cat' with 'dog' in a string, but only if 'cat' is a whole word (not part of 'category'). Which code achieves this?

Accepted Answer

re.sub(r'\bcat\b', 'dog', s). Uses the `re.sub()` function with the regex pattern `r'\bcat\b'`, where `\b` denotes a word boundary. This ensures that only the whole word 'cat' is matched and replaced with 'dog', ignoring cases where 'cat' appears as part of a larger word like 'category'. The `r` prefix makes it a raw string, preventing escape sequence issues.

Answer

s.replace('cat', 'dog')

Answer

re.sub('cat', 'dog', s)

Answer

s.replace('cat', 'dog', 1)

Question 14

Which string method would you use to check if a string starts with a specified prefix?

Accepted Answer

startswith(). The correct method to check if a string starts with a specified prefix in Python is `str.startswith()`. It returns `True` if the string begins with the given prefix, otherwise `False`. This method is part of the standard string methods in Python and is case-sensitive by default.

Answer

start_with()

Answer

beginswith()

Answer

startwithcase()

Question 15

What will be printed?

Accepted Answer

None. None. This question likely tests that Python functions return None by default when no explicit return statement is present, and printing that value yields None. Therefore, option D is correct.

Answer

-1

Answer

0

Answer

An exception is raised.