PCAP Practice Exam 2 — 20 Questions

Question 1

Which of the following is the BEST practice for building a large string by concatenating many smaller strings in Python?

Accepted Answer

result = ''.join(parts). `''.join(parts)` is the most efficient way to concatenate a large number of strings in Python. It allocates memory once for the final string by iterating over the list and copying each part into the result buffer, avoiding the O(n²) time complexity of repeated concatenation in a loop.

Answer

result = sum(parts, '')

Answer

result = str.concat(*parts)

Answer

result = ''; for part in parts: result += part

Question 2

A developer has two separate directories on sys.path: /home/user/libs and /opt/libs. Both directories contain a subdirectory 'mypackage' without an __init__.py file. The developer wants to import a module from 'mypackage' that exists only in one of the directories. What concept allows Python to treat these two directories as a single namespace package?

Accepted Answer

Implicit namespace packages (PEP 420). PEP 420 introduced implicit namespace packages, which allow multiple directories on sys.path to contribute to the same package without requiring __init__.py files. When Python encounters a directory without __init__.py, it treats it as a namespace package, merging all matching directories across sys.path into a single logical package. This enables the developer to import a module from 'mypackage' that exists in only one of the directories, as Python searches all paths and resolves the module from the first location where it is found.

Answer

Regular packages with __init__.py

Answer

sys.path merging

Answer

Package overriding

Question 3

Which TWO of the following statements about Python's `sys.path` are true?

Accepted Answer

Module search stops at the first matching directory in `sys.path`.. Python's import mechanism iterates through `sys.path` in order and stops at the first directory containing the requested module. Option E is correct: the directory containing the script (or the current directory when running interactively) is inserted at the beginning of `sys.path` at startup. Options A, C, and D are false: the current working directory is not always first (the script's directory takes precedence), `sys.path` is initialized from the `PYTHONPATH` environment variable *in addition to* default paths, and `sys.path` is a list, not a tuple. Therefore, only two statements are true.

Answer

The current working directory is always the first element in `sys.path`.

Answer

`sys.path` is initialized from the PYTHONPATH environment variable.

Answer

`sys.path` is a tuple of strings.

Question 4

What is the result of the expression '12345'[:10]?

Accepted Answer

'12345'. In Python, slicing a string with a start index of 0 and an end index of 10 (as in '12345'[:10]) returns the entire string if the slice end exceeds the string length. Since '12345' has only 5 characters, the slice extracts all characters without padding or error, resulting in '12345'.

Answer

'12345     '

Answer

IndexError

Answer

'12345 '

Question 5

A user wants to ensure that a custom module 'mymod' located at '/home/user/custom' takes precedence over a standard library module with the same name. Which operation on sys.path should be performed?

Accepted Answer

sys.path.insert(0, '/home/user/custom'). `sys.path.insert(0, '/home/user/custom')` adds the custom module's directory to the very beginning of the module search path. Python's import system scans `sys.path` in order, so placing the custom directory first ensures that `mymod` is found there before any standard library or site-packages directory that might contain a module with the same name.

Answer

sys.path.replace('/', '/home/user/custom')

Answer

sys.path.append('/home/user/custom')

Answer

sys.prefix = '/home/user/custom'

Question 6

Refer to the exhibit. What is the root cause of the error?

Accepted Answer

The attribute 'age' is not defined in the class or instance.. The error 'AttributeError: 'ClassName' object has no attribute 'age'' occurs when code attempts to access an instance attribute that has never been defined. In Python, attributes must be assigned (e.g., in __init__ or directly on the instance) before they can be read; simply declaring a class-level variable named 'age' would not cause this error, but if no assignment exists, the attribute is missing.

Answer

The __init__ method was not called.

Answer

The attribute 'age' is private.

Answer

The attribute 'age' is a class attribute but not initialized.

Question 7

What is the output of the following code? s = 'Hello'; print(s.find('l'))

Accepted Answer

2. The `str.find()` method returns the lowest index of the first occurrence of the substring. In the string 'Hello', the character 'l' first appears at index 2 (0-based indexing: H=0, e=1, l=2). Therefore, `s.find('l')` returns 2, making option B correct.

Answer

1

Answer

0

Answer

3

Question 8

A developer wants to ensure that a class attribute is shared across all instances. Which approach should be used?

Accepted Answer

Define the attribute in the class body, outside any methods.. Defining an attribute in the class body, outside any methods, creates a class attribute that is shared across all instances. Class attributes are stored in the class's __dict__ and are accessible via the class or any instance, unless shadowed by an instance attribute.

Answer

Use the @property decorator.

Answer

Define the attribute inside a method without using self.

Answer

Define the attribute inside __init__ using self.

Question 9

A developer creates a Python class with a method that is intended to be overridden in subclasses. Which approach best ensures that the method is not accidentally called on the base class?

Accepted Answer

Raise NotImplementedError inside the method body. Raising NotImplementedError inside the base class method is the standard Python idiom for defining an abstract-like method that must be overridden in subclasses. If a subclass fails to override the method and it is called, Python will raise an explicit error at runtime, preventing accidental use of the base implementation. This approach enforces the contract that the method is intended only for subclasses, without requiring the `abc` module.

Answer

Use 'pass' as the method body

Answer

Delete the method from the base class using 'del'

Answer

Add a comment '# override in subclass' inside the method body

Question 10

Which THREE factors can cause an 'ImportError' when trying to import a module?

Accepted Answer

The module is a C extension that fails to load.. If a module is a C extension (e.g., a .so or .pyd file) and it fails to load due to missing dependencies, incompatible architecture, or a linking error, Python raises an ImportError. This is distinct from a syntax error in Python source code, which would raise a SyntaxError, not an ImportError.

Answer

The module file has a syntax error.

Answer

The module's __init__.py is empty.

Question 11

What is the likely outcome of running the following code?

```python
with open("C:\Users\path\file.txt", "r") as f:
    print(f.read())
```

Accepted Answer

The program raises a SyntaxError due to invalid escape sequences.. The code likely contains backslash sequences (e.g., `\U`, `\p`, or other non-standard escapes) that are not valid escape sequences in Python. Starting with Python 3.12, such invalid sequences raise a `SyntaxError` at compile time, preventing the program from running. In earlier versions, a `DeprecationWarning` is issued, but the code may run. The error is not about file operations or path resolution; it's a compile-time syntax error. To avoid this, use raw strings (`r"..."`) or double backslashes (`\`).

Answer

The program runs but the file contents are incorrect.

Answer

The program raises a FileNotFoundError because the path is invalid after escape interpretation.

Answer

The file is opened successfully because backslashes are ignored.

Question 12

A package 'mypkg' has the following structure:
mypkg/
  __init__.py
  submod1.py
  submod2.py
The __init__.py file contains: from . import submod1, submod2. A user runs 'import mypkg' and then 'mypkg.submod1.func()'. However, the user got an AttributeError. What is the most likely cause?

Accepted Answer

The submod1 module does not define a function named 'func'.. The AttributeError indicates that the attribute 'func' was not found on the module object 'submod1'. Since the import statement in __init__.py correctly makes submod1 accessible as mypkg.submod1, the only remaining reason for the error is that submod1.py does not define a function named 'func'. The import mechanism itself is working as intended.

Answer

submod1 is actually a package, not a module, so it cannot be called with 'func()'.

Answer

The __init__.py should use absolute imports like 'import mypkg.submod1' to make submod1 accessible.

Answer

The user must also run 'from mypkg import submod1' before accessing submod1.

Question 13

Drag and drop the steps to define and call a function with default arguments in Python into the correct order.

Accepted Answer

Use the def keyword followed by the function name and parentheses
Specify parameters with default values using the assignment operator
Include a colon and indent the function body
Write the function body with statements that use the parameters
Call the function with only required arguments to use default values
Call the function with all arguments to override defaults. To define a function with default arguments in Python, first use the def keyword, then provide the function name and parentheses. Inside the parentheses, specify any parameters, optionally assigning default values using the assignment operator. Follow with a colon and indent the function body. Finally, call the function by its name, passing arguments as needed. The correct order is 1,2,3,4,5,6.

Answer

Call the function with all arguments to override defaults
Use the def keyword followed by the function name and parentheses
Specify parameters with default values using the assignment operator
Include a colon and indent the function body
Write the function body with statements that use the parameters
Call the function with only required arguments to use default values

Answer

Use the def keyword followed by the function name and parentheses
Specify parameters with default values using the assignment operator
Include a colon and indent the function body
Call the function with only required arguments to use default values
Write the function body with statements that use the parameters
Call the function with all arguments to override defaults

Answer

Use the def keyword followed by the function name and parentheses
Include a colon and indent the function body
Specify parameters with default values using the assignment operator
Write the function body with statements that use the parameters
Call the function with only required arguments to use default values
Call the function with all arguments to override defaults

Question 14

You are a network engineer troubleshooting a script that processes router configuration files. The script reads a configuration line from a file: 'interface GigabitEthernet0/1
 ip address 192.168.1.1 255.255.255.0
 no shutdown'. The script needs to extract the interface name and IP address. The current code uses string split operations but fails when the line has extra spaces or tabs. For example, when the line is 'interface   GigabitEthernet0/1', the split returns ['interface', '', '', 'GigabitEthernet0/1'] and the script fails. You need to modify the script to robustly extract the interface name and IP address regardless of whitespace. Which approach should you take?

Accepted Answer

Use line.split() instead of line.split(' ').. `line.split()` without arguments splits on any whitespace (spaces, tabs, newlines) and automatically removes empty strings, making it robust against extra spaces or tabs. In contrast, `line.split(' ')` splits only on single space characters, leaving empty strings when multiple spaces or tabs are present. This behavior is defined by Python's string method documentation and is essential for parsing configuration files where whitespace is inconsistent.

Answer

Manually iterate and concatenate characters until a space is found.

Answer

Use line.split(' ') and then filter out empty strings.

Answer

Use line.startswith('interface') to identify the line, then extract substring.

Question 15

A developer wants to implement a read-only property for a class 'Temperature' that returns the temperature in Celsius but prevents external modification. Which code snippet correctly defines such a property?

Accepted Answer

class Temperature: @property
def celsius(self): return self._celsius. It defines a read-only property using the `@property` decorator with only a getter method. Without a setter, any attempt to assign a value to `celsius` will raise an `AttributeError`, making the property read-only. This is the standard Pythonic way to implement a read-only attribute.

Answer

class Temperature: @property
def celsius(self): return self._celsius
@celsius.setter
def celsius(self, val): self._celsius = val

Answer

class Temperature: def __setattr__(self, name, val): if name == 'celsius': raise AttributeError

Answer

class Temperature: def __init__(self, c): self.celsius = c

Question 16

A developer is writing a function to reverse each word in a sentence while preserving the original order of the words. For example, 'Hello World' should become 'olleH dlroW'. The current implementation is: def reverse_words(s): return ' '.join(word[::-1] for word in s.split()). This works for simple cases. However, the input may contain multiple spaces between words (e.g., 'Hello   World') and tabs. The requirement is to preserve the exact whitespace between words (including tabs and multiple spaces) in the output. Which of the following modifications will achieve this while keeping the approach efficient?

Accepted Answer

Use re.split(r'(\s+)', s) to separate words and whitespace, then reverse the word parts and join back. `re.split(r'(\s+)', s)` splits the string into a list where every other element is a whitespace segment (preserving exact spaces and tabs), and the word segments can be reversed individually. Joining the list back with `''.join(...)` reconstructs the original whitespace exactly, meeting the requirement efficiently without manual iteration.

Answer

Use s.split(' ') and handle empty strings to preserve spaces, but ignore tabs

Answer

Iterate over the string, detect word boundaries, and build a new string manually

Answer

Use s.split() and then join with the original spaces using a separate loop that tracks whitespace

Question 17

A developer needs to write binary data to a file. Which file mode should be used to open the file for writing in binary mode without truncating it if it already exists?

Accepted Answer

'ab'. ('ab') is correct because the 'a' mode opens the file for appending, which writes data at the end without truncating the existing content, and adding 'b' specifies binary mode. This allows binary data to be written to a file that already exists without losing its current contents.

Answer

'wb'

Answer

'rb'

Answer

'wb+'

Question 18

A developer wants to check if a string 'example.txt' ends with '.txt'. Which expression returns True?

Accepted Answer

'example.txt'.endswith('.txt'). The `endswith()` method is specifically designed to check if a string ends with a given suffix. In this case, `'example.txt'.endswith('.txt')` returns `True` because the string ends with the substring '.txt'.

Answer

'example.txt'.startswith('.txt')

Answer

'example.txt'.find('.txt')

Answer

'example.txt'.rsplit('.',1)

Question 19

Which of the following exception classes is NOT a direct subclass of Exception in Python?

Accepted Answer

SystemExit. SystemExit is not a direct subclass of Exception; it inherits from BaseException instead. This is because SystemExit, along with KeyboardInterrupt and GeneratorExit, is intended to signal that the interpreter should exit, and catching it with a generic except Exception clause would be inappropriate. All other options (IOError, StopIteration, ValueError) are direct subclasses of Exception.

Answer

IOError

Answer

StopIteration

Answer

ValueError

Question 20

Which of the following expressions returns the string 'Hello' repeated three times?

Accepted Answer

'Hello' * 3. In Python, the multiplication operator (*) when used with a string and an integer performs string repetition. 'Hello' * 3 returns the string 'HelloHelloHello' by concatenating three copies of the original string. This is a core feature of Python's sequence protocol, where strings are sequences of characters.

Answer

'Hello' + 3

Answer

'Hello' * '3'

Answer

'Hello' * 3.0