PCPP1 Library Modules Practice Test 2 — 15 Questions

Question 1

You are working with the os module to manipulate file paths in a cross-platform Python application. You need to perform operations that are portable across Windows and Unix-like systems. Which TWO of the following are valid and recommended uses of the os.path submodule for path manipulation? (Choose two.)

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

os.path.join('folder', 'file.txt') to construct a path using the correct separator for the current OS.. os.path.join() and os.path.split() are fundamental for portable path manipulation. join constructs paths using the correct separator, and split separates the directory and filename. These functions abstract away platform differences, making code cross-platform. Other functions like isdir, abspath, and normpath are useful but not the primary recommended uses for path manipulation in the context of the question.

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os.path.abspath('file.txt') to convert a relative path to an absolute path based on the current working directory.

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os.path.normpath('folder//file.txt') to normalize a path by collapsing redundant separators.

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os.path.isdir('C:\Users\file.txt') to check if a path is a directory, regardless of the operating system.

Question 2

You are writing a Python script that needs to parse a JSON string containing a date in ISO 8601 format. You want to automatically convert this date string into a datetime.date object during parsing. Which of the following approaches using the json module is correct?

Accepted Answer

Pass a function to the object_hook parameter of json.loads that checks if the key is 'date' and returns a datetime.date object.. To convert date strings during JSON parsing, you should use the object_hook parameter of json.loads. This parameter allows you to specify a function that is called with each decoded JSON object (dictionary), enabling you to transform values, such as converting a date string to a datetime.date object. The other parameters are for specific types (floats, ints) or for serialization (default).

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Use the parse_float parameter to specify a function that converts date strings to datetime.date objects.

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Use the default parameter of json.loads to provide a function that converts date strings to datetime.date objects.

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Use the parse_int parameter to specify a function that recognizes date strings and converts them.

Question 3

You are writing a Python script to monitor a directory. When a new file appears, you need to read its last line efficiently without loading the entire file into memory. The files can be very large (several gigabytes). Which approach using the os module is most appropriate?

Accepted Answer

Use os.stat() to get the file size, then open the file in binary mode and seek to a position near the end to read the last line.. The correct approach uses os.stat() to get the file size, then opens the file in binary mode and seeks to a position near the end. This avoids reading the entire file, which is crucial for very large files. It leverages the os module's file metadata capabilities while using standard file I/O for efficient reading.

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Use os.path.getsize() to check the file size, then if it is small enough, read the whole file; otherwise, raise an exception.

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Use os.open() with the os.O_RDONLY flag to get a file descriptor, then call os.lseek() to move to the end and os.read() to read backwards until a newline is found.

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Use os.read() to read the entire file content into a bytes object, then split by newline and take the last element.

Question 4

You are using the `os` module to manipulate file paths in a cross-platform script. You need to extract the filename without extension from a path, and also check if a path is absolute. Which TWO of the following statements about the `os.path` module are correct? (Choose two.)

Accepted Answer

`os.path.basename('/home/user/file.txt')` returns `'file.txt'`.. The correct statements are that `os.path.splitext` splits the extension correctly, and `os.path.basename` returns the filename. These are fundamental behaviors of the `os.path` module. The other options contain misconceptions about absolute paths, cross-platform joining, and normalization details.

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`os.path.normpath('home/../user/file.txt')` returns `'user/file.txt'`.

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`os.path.isabs('C:\Users\file.txt')` returns `True` on Windows.

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`os.path.join('home', 'user', 'file.txt')` returns `'home/user/file.txt'` on all platforms.

Question 5

You are designing a class that needs to support the context manager protocol. The class manages a network connection that must be closed exactly once, even if multiple exceptions occur within the with block. Which implementation correctly ensures that the connection is closed and that any exception is propagated?

Accepted Answer

Define __enter__ to return self and __exit__ to close the connection and return False.. The correct implementation defines __enter__ to return self and __exit__ to close the connection and return False. This ensures the connection is closed exactly once when the with block exits, and any exception is propagated because returning False does not suppress it. This adheres to the context manager protocol.

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Define __enter__ to return self and __exit__ to close the connection and return True.

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Define __enter__ to close the connection and return self, and __exit__ to do nothing.

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Define __enter__ to return self and __exit__ to close the connection and re-raise the exception if one occurred.

Question 6

You are using xml.etree.ElementTree to parse a large XML document. You need to find all 'book' elements that are descendants of any 'section' element, but you must not include 'book' elements that are direct children of the root. Which XPath expression correctly achieves this?

Accepted Answer

root.findall('.//section//book'). The goal is to select all 'book' elements that have a 'section' ancestor, while excluding those that are direct children of the root. The expression './/section//book' uses the descendant-or-self axis for both 'section' and 'book', ensuring that any book under any section is included, regardless of nesting depth. Other expressions either include all books, restrict to direct children, or limit to immediate children of sections.

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root.findall('./section/book')

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root.findall('.//book')

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root.findall('.//section/book')

Question 7

You are writing a Python script that needs to read a text file and count the number of lines. The file may be very large, so you want to avoid loading it entirely into memory. Which approach using the os module is most efficient?

Accepted Answer

Open the file with open() and iterate over it line by line, incrementing a counter for each line.. The most efficient approach is to open the file and iterate over it line by line, which reads lazily and counts exactly without loading the entire file into memory. This is the recommended pattern for processing large text files in Python.

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Use os.path.getsize() to get the file size and divide by an average line length to estimate the line count.

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Use os.read() to read the entire file into a string, then use the count() method to count newline characters.

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Use os.stat() to get the file size, then open the file and use seek() to jump to the end and read backwards counting newlines.

Question 8

You are maintaining a Python 3 application that must read a JSON configuration file containing comments and trailing commas, which the standard json module cannot parse. You need to parse this file while preserving the comment information for later use. Which approach should you take?

Accepted Answer

Use the json5 library to parse the file, which supports comments and trailing commas and provides the parsed data as Python objects.. The json5 library is designed to parse JSON5, a superset of JSON that includes comments and trailing commas. It successfully parses such files into Python objects. While it does not retain comments in the output, it is the only option that correctly handles the syntax. The other options either fail to parse the file or discard comments without preserving them.

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Use the configparser module to read the file, as it supports comments and can handle JSON-like structures.

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Read the file line by line and strip lines starting with # or // before passing the cleaned text to json.loads().

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Use json.load() with the strict=False parameter to allow comments and trailing commas.

Question 9

You are using the sqlite3 module to interact with a database. You need to execute a query that inserts multiple rows efficiently and then retrieve the auto-generated primary key of the last inserted row. Which combination of methods should you use?

Accepted Answer

Use cursor.execute() with a single INSERT statement containing multiple VALUES clauses, then cursor.lastrowid to get the ID of the last inserted row.. A single INSERT statement with multiple VALUES clauses is both efficient and allows retrieval of the last inserted row ID via cursor.lastrowid. This attribute is updated after each successful INSERT and returns the rowid of the last row inserted by that statement. Using executemany() is efficient for insertion but does not provide a reliable way to get the last inserted ID, and executescript() has transaction implications that make it unsuitable.

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Use cursor.executescript() to run multiple INSERT statements, then cursor.lastrowid to get the last inserted row ID.

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Use cursor.execute() to insert each row in a loop, then cursor.lastrowid after each insert to collect the IDs.

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Use cursor.executemany() to insert the rows, then cursor.lastrowid to get the last inserted row ID.

Question 10

When using sqlite3.Row, what is the primary benefit over using a standard tuple?

Accepted Answer

It provides dictionary-like access to columns by name.. sqlite3.Row allows accessing column values by name (string keys) instead of just numerical indices.

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It automatically commits transactions.

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It is faster to execute.

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It supports multi-threading natively.

Question 11

You are using configparser.ConfigParser to read a configuration file. You have a file where option names are case-sensitive. How do you ensure the parser respects this casing?

Accepted Answer

parser.optionxform = lambda x: x. By default, ConfigParser converts keys to lowercase. You must override the optionxform method of the parser instance.

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parser = ConfigParser(case_sensitive=True)

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parser.set_case(True)

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parser.read(file, case='preserve')

Question 12

You are processing a CSV file using csv.DictReader. If your input file lacks a header row, how do you provide the field names?

Accepted Answer

csv.DictReader(f, fieldnames=['a', 'b']). You pass the 'fieldnames' argument to the constructor to define the headers explicitly.

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csv.DictReader(f, headers=['a', 'b'])

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csv.DictReader(f).map(['a', 'b'])

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csv.DictReader(f, columns=['a', 'b'])

Question 13

Which method in the xml.dom.minidom module is used to retrieve the value of a specific attribute of an element?

Accepted Answer

element.getAttribute('attr_name'). The getAttribute() method is used to retrieve the value of an attribute by its name.

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element.attr('attr_name')

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element.getAttributeNode('attr_name').value

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element.value('attr_name')

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element['attr_name']

Question 14

You need to configure the logging module to capture logs from multiple modules while ensuring that logs from third-party libraries (e.g., 'urllib3') are only captured at the WARNING level. How do you set this?

Accepted Answer

logging.getLogger('urllib3').setLevel(logging.WARNING). You can configure individual loggers using getLogger() and setting their specific level attribute.

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logging.config.dictConfig({'urllib3': 'WARNING'})

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logging.basicConfig(level=logging.WARNING)

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logging.setLevel('urllib3', logging.WARNING)

Question 15

You are using the sqlite3 module to manage a database. You need to ensure that database changes are permanently saved even if your script terminates unexpectedly. Which method should you call after an INSERT operation?

Accepted Answer

connection.commit(). The commit() method on a connection object is required to save changes permanently in sqlite3.

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connection.save()

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cursor.flush()

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connection.close()