PCAP Practice Test 3 — 10 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

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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.