PCAP Practice Test 26 — 15 Questions

Question 1

Refer to the exhibit. Which THREE statements about the class hierarchy are correct?

Accepted Answer

Calling D().method() returns 'B'. When `D().method()` is called, Python's MRO (Method Resolution Order) for class D is `['D', 'B', 'C', 'A', 'object']`. Since class D does not define `method`, Python looks up the MRO and finds `method` first in class B. The `return 'B'` in B's `method` is executed, so the call returns 'B'.

Answer

D does not have a method named 'method'

Answer

The super() call in B would call C.method

Question 2

Which TWO of the following methods return a boolean value?

Accepted Answer

str.isspace(). The methods `str.isspace()` and `str.isalpha()` are both string methods that return a boolean value (`True` or `False`) based on whether the string meets specific character classification criteria. `isspace()` returns `True` if all characters in the string are whitespace, while `isalpha()` returns `True` if all characters are alphabetic.

Answer

str.upper()

Answer

str.split()

Answer

str.join()

Question 3

A Python application processes user-uploaded files. The requirement is to catch any I/O-related exception while reading the file, but not to catch KeyboardInterrupt or SystemExit. Which exception type should be caught?

Accepted Answer

OSError. `OSError` is the base class for all I/O-related exceptions in Python 3, including file reading errors like `FileNotFoundError` and `PermissionError`. It does not catch `KeyboardInterrupt` or `SystemExit`, which inherit directly from `BaseException`, not `Exception`. This makes `OSError` the precise choice for catching I/O errors while allowing program termination signals to propagate.

Answer

IOError

Answer

Exception

Answer

BaseException

Question 4

A developer wants to remove leading and trailing whitespace from a string. Which method should be used?

Accepted Answer

s.strip(). The `strip()` method in Python removes both leading and trailing whitespace (including spaces, tabs, and newlines) from a string. This is the standard method for trimming whitespace from both ends, as specified in Python's string documentation.

Answer

s.lstrip()

Answer

s.trim()

Answer

s.rstrip()

Question 5

Which string method can be used to check if a string contains only digits?

Accepted Answer

str.isdigit(). The `str.isdigit()` method returns `True` if all characters in the string are digits (0-9) and the string is non-empty. This is the most direct and commonly used method for checking numeric-only strings in Python, as it specifically tests for digit characters without including other numeric forms like fractions or Roman numerals.

Answer

str.isalnum()

Answer

str.isdecimal()

Answer

str.isnumeric()

Question 6

A logging module receives a message that may contain sensitive data. To comply with data privacy, all digits in the message should be replaced with 'X' before logging. Which approach correctly achieves this?

Accepted Answer

re.sub(r'[0-9]', 'X', message). Options B, C, and D all correctly replace all digits in the message with 'X'. Option B uses `re.sub()` with a regex character class to match any digit. Option C uses `str.translate()` with a mapping from each digit to 'X', which works because the mapping explicitly covers all digits. Option D uses a list comprehension with `isdigit()` to conditionally replace digits. Option A is incorrect because `str.replace()` does not interpret character ranges; it would look for the literal string '0-9'. Therefore, three correct approaches exist.

Answer

message.replace('0-9', 'X')

Question 7

What is the result of the expression 'aBc'.lower()?

Accepted Answer

'abc'. The `lower()` method returns a new string with all cased characters converted to lowercase. Since the original string 'aBc' contains an uppercase 'B', calling `.lower()` converts it to 'b', resulting in 'abc'. The method does not modify the original string but returns a new one.

Answer

'Abc'

Answer

'aBc'

Answer

'ABC'

Question 8

Which TWO of the following string methods modify the string in place? (Note: Python strings are immutable.)

Accepted Answer

str.lower(). None of the listed string methods modify the string in place because Python strings are immutable. All string methods return a new string rather than altering the original. Therefore, there are no correct options for this question.

Answer

str.join()

Answer

str.replace()

Answer

str.strip()

Question 9

A developer defines a class 'A' with a method 'm' that uses 'self.a'. Class 'B' inherits from 'A' and defines __init__ that sets 'self.a = 10'. An instance of B is created and method m is called. What is the output?

Accepted Answer

10. When an instance of class B is created, its __init__ method sets self.a = 10. When method m (inherited from A) is called on that instance, self refers to the B instance, so self.a resolves to 10. Python's attribute lookup follows the instance's __dict__ first, finding the attribute set by B's __init__.

Answer

None

Answer

AttributeError

Answer

0

Question 10

A data scientist needs to count the occurrences of a substring in a long DNA sequence (e.g., 1 million bases). However, the count must include overlapping occurrences. For example, in 'AAAA', the substring 'AA' appears three times overlapping. The built-in count() method does not count overlapping matches. The scientist needs a function to count overlapping substrings efficiently without using third-party libraries. Which of the following approaches is the most efficient for this task?

Accepted Answer

Use re.findall with a positive lookahead: len(re.findall(r'(?=AA)', sequence)). `re.findall` with a positive lookahead `(?=AA)` matches overlapping occurrences without consuming characters. The lookahead assertion checks for the substring at each position without advancing the match position, so every overlapping occurrence is found. This is more efficient than manual loops because the underlying regex engine is implemented in C and optimized for pattern matching.

Answer

Use a for loop with slicing and compare: sum(1 for i in range(len(s)-len(sub)+1) if s[i:i+len(sub)] == sub)

Answer

Use two nested loops to check all possible positions

Answer

Use a while loop with str.find() and increment the start index by 1

Question 11

A developer writes: s = 'abc'; s[0] = 'x'. What happens?

Accepted Answer

TypeError: 'str' object does not support item assignment. In Python, strings are immutable, meaning their contents cannot be changed after creation. Attempting to assign a new character to an index position (e.g., `s[0] = 'x'`) raises a `TypeError: 'str' object does not support item assignment`. This is a fundamental property of the `str` type in Python, enforced at the interpreter level.

Answer

s becomes 'xbc'

Answer

ValueError: string index out of range

Answer

s becomes 'abc' and no error

Question 12

What is the output of the code?

Accepted Answer

20. The `Derived` class inherits the `get_x` method from the `Base` class, which returns `self._x`. When `obj.get_x()` is called, `self` refers to the `Derived` instance, and `self._x` accesses the `_x` attribute set in `Derived.__init__` (value 20). The `_x` attribute in `Derived` shadows the one in `Base`, so the output is 20.

Answer

AttributeError: 'Derived' object has no attribute 'get_x'

Answer

10

Answer

AttributeError: 'Derived' object has no attribute '_x'

Question 13

Consider the following directory structure:
project/
  main.py
  pkg/
    __init__.py
    mod1.py
    subpkg/
      __init__.py
      mod2.py
From main.py, you write: from pkg.subpkg import mod2
Which THREE of the following are true regarding relative imports?

Accepted Answer

Relative imports only work when the importing module is part of a package.. Relative imports (using dot notation like `..` or `.`) are only valid when the importing module is itself part of a package. This is because relative imports rely on the `__package__` attribute to resolve the import path; if the module is not inside a package (e.g., a top-level script), `__package__` is `None` or empty, and relative imports will raise an `ImportError`.

Answer

In main.py, you can use `from . import pkg` to import pkg.

Answer

A directory must contain an __init__.py file to be a package for relative imports to function.

Question 14

Which TWO statements about the sys module are true?

Accepted Answer

sys.exit() raises SystemExit with a default exit code of 0.. `sys.exit()` raises the `SystemExit` exception, and when called without an argument, the default exit code is 0, indicating successful termination. This behavior is defined in the Python documentation for the `sys` module.

Answer

sys.path is a tuple of module search paths.

Answer

sys.modules is a list of all loaded modules.

Answer

The sys module is automatically imported in every Python script.

Question 15

A developer runs 'pip install mypackage' but gets a 'PermissionError'. Which command should be used to install the package for the current user only?

Accepted Answer

pip install --user mypackage. The `--user` flag instructs pip to install the package into the user's site-packages directory (e.g., `~/.local/lib/pythonX.Y/site-packages` on Unix), which does not require elevated permissions. This avoids the `PermissionError` that occurs when pip tries to write to the system-wide site-packages directory (e.g., `/usr/lib/python3/dist-packages`) without administrator privileges.

Answer

sudo pip install mypackage

Answer

pip install --ignore-installed mypackage

Answer

pip install --target mypackage