PCPP1 Practice Test 19 — 15 Questions

Question 1

When using 'requests.get()', how can you include a custom HTTP header in your request?

Accepted Answer

Use the 'headers' dictionary argument. The 'headers' parameter accepts a dictionary of HTTP headers.

Answer

Use the 'data' argument

Answer

Pass it as part of the URL string

Answer

Use the 'params' dictionary

Question 2

A Tkinter data-entry form uses an Entry widget for a numeric amount. Users report that pressing Enter in the Entry does nothing, and the value is only saved when they click a separate Save button. You want Enter to trigger the same save routine as the button, without duplicating logic. Which binding achieves this?

Accepted Answer

entry.bind('', lambda event: save_amount()). The event sequence is the correct Tkinter binding for the Enter key on an Entry widget. Binding it to a small lambda that calls the existing save function reuses the button's logic and gives users the keyboard shortcut they expect. KeyPress is too broad, Enter refers to pointer entry, and FocusOut triggers on focus changes rather than the Enter key.

Answer

entry.bind('<KeyPress>', lambda event: save_amount())

Answer

entry.bind('<Enter>', lambda event: save_amount())

Answer

entry.bind('<FocusOut>', lambda event: save_amount())

Question 3

What is the recommended way to handle a function that requires a large number of arguments?

Accepted Answer

Group related parameters into a dataclass or object.. If a function has too many arguments, it is often a sign it should be broken down or that a configuration object should be used.

Answer

Just define the function with many arguments; it is perfectly fine.

Answer

Use a single argument dictionary.

Answer

Use *args and **kwargs for everything.

Question 4

You need to send binary data over a socket. Which method should you use on the socket object to ensure all data is sent?

Accepted Answer

sendall(). The sendall() method continues to transmit data from the buffer until all data has been sent or an error occurs.

Answer

write()

Answer

send()

Answer

recv()

Question 5

In the context of the CSV module, what is a 'dialect'?

Accepted Answer

A set of parameters defining a CSV format.. A dialect is a grouping of parameters (delimiter, quotechar, etc.) that defines the format of a CSV file.

Answer

A specific file extension.

Answer

The encoding of the file.

Answer

A list of column names.

Question 6

Which status code indicates that a requested resource has been successfully created?

Accepted Answer

201 Created. HTTP status code 201 Created indicates that the request has succeeded and has led to the creation of a new resource. It is typically returned in response to a POST or PUT request that creates a resource, and the response often includes a Location header pointing to the new resource. This is the standard, RFC 7231-defined code for successful resource creation.

Answer

400 Bad Request

Answer

200 OK

Answer

204 No Content

Question 7

You are developing a Tkinter application that uses multiple threads to perform background tasks. One thread updates a Label widget's text using its config method. Occasionally, the application crashes with a Tcl error about calling from a different thread. What is the correct approach to safely update the GUI from a background thread?

Accepted Answer

Use the after method to schedule the update on the main thread.. Tkinter is not thread-safe; all GUI updates must occur in the main thread. To safely update a widget from a background thread, you should use the after method to schedule a callback that performs the update. This callback runs in the main event loop. Other approaches like using locks or update_idletasks do not address the fundamental thread safety issue. Direct calls from background threads are unsafe.

Answer

Directly call the widget's config method from the background thread; Tkinter handles thread safety internally.

Answer

Use a lock (threading.Lock) around the widget update to prevent concurrent access.

Answer

Call update_idletasks() before updating the widget from the background thread.

Question 8

A developer is writing a Python function that accepts a mutable default argument, such as `def add_item(item, items=[])`. A code reviewer flags this as a potential bug. Which statement best explains the issue and the recommended fix according to best practices?

Accepted Answer

The default list is shared across all calls, so use `None` as the default and create a new list inside the function.. Mutable default arguments are evaluated once at definition time, causing shared state across calls. The correct practice is to use `None` as a default and create a new mutable object inside the function. This avoids bugs where data unexpectedly persists. Other options either misdiagnose the problem or propose ineffective solutions.

Answer

The default list is copied for each call, so the only issue is performance; use a tuple for efficiency.

Answer

The default list is immutable, so it cannot be modified; use a tuple instead.

Answer

The default argument is re-evaluated on each call, so the code is safe; no change is needed.

Question 9

You are building a Tkinter application with a Button widget that should run a long-running calculation when clicked, but the GUI freezes until the calculation finishes. Which approach best keeps the interface responsive while performing the calculation?

Accepted Answer

Run the calculation in a separate thread and update the GUI using a thread-safe mechanism such as a queue polled by after().. Tkinter widgets must be manipulated from the thread that created the Tk instance, which is normally the main thread running mainloop(). Performing a long computation in a button callback monopolizes that thread, freezing the interface. The reliable pattern is to execute the computation in a worker thread and pass results back through a thread-safe queue that the main thread inspects with after(). This keeps the event loop cycling and the GUI responsive.

Answer

Call update_idletasks() inside the calculation loop to refresh the window.

Answer

Call the calculation function directly inside the button's command callback.

Answer

Use the after() method with a delay of zero to schedule the calculation repeatedly.

Question 10

You need to add a label that displays static text in your GUI. Which widget is most appropriate for this purpose?

Accepted Answer

tk.Label(). tk.Label() is the canonical Tkinter widget for displaying static, non-editable text (or images) in a GUI. It supports options like text, font, fg, bg, and anchor, and is designed specifically for read-only display. For multi-line static text, tk.Message() is a variant, but tk.Label() is the general-purpose choice.

Answer

tk.Message()

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tk.Entry()

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tk.Display()

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tk.Text()

Question 11

You need to perform a HEAD request to check if a file exists on a server without downloading the body. How is this done with 'requests'?

Accepted Answer

requests.head(url). The requests.head() method sends a HEAD request, which only retrieves headers.

Answer

requests.post(url, data={'type': 'head'})

Answer

requests.options(url)

Answer

requests.get(url, headers={'Method': 'HEAD'})

Question 12

You are working with a large XML file and need to extract specific elements efficiently without loading the entire document into memory. You decide to use the xml.etree.ElementTree module. Which of the following methods should you use to iterate over all 'book' elements in the document?

Accepted Answer

Use the iterparse() function to process the XML incrementally and handle 'end' events for 'book' tags.. For memory-efficient parsing of large XML files, iterparse() is the recommended function. It allows incremental processing by generating events as elements are parsed. By handling 'end' events for 'book' tags and clearing elements, you can extract data without loading the entire document. The other methods load the full document into memory, which is inefficient for large files.

Answer

Use the findall() method on the root element to retrieve all 'book' elements at once.

Answer

Use the XMLPullParser to pull events and process 'book' elements as they are encountered.

Answer

Use the parse() function and then iterate over the tree using a for loop.

Question 13

In a multithreaded network application, you observe 'ConnectionResetError'. What is the most likely cause when using Python sockets?

Accepted Answer

The remote server closed the connection abruptly. This occurs when the remote host closes the connection while the local end is still trying to send or receive data.

Answer

The port is already in use by another process

Answer

The socket was never bound

Answer

The local thread pool is exhausted

Question 14

What is the purpose of the 'weakref' module in relation to the Observer pattern?

Accepted Answer

To prevent memory leaks.. It allows the subject to maintain references to observers without preventing their collection by the garbage collector.

Answer

To allow private access to observers.

Answer

To ensure thread safety.

Answer

To serialize observers.

Question 15

You are writing a Python tool that must connect to a REST API over HTTPS. The API's server certificate is signed by an internal corporate CA whose root certificate is stored in a file named corp-ca.pem. You use the requests library and need the connection to be verified against that specific CA while still performing normal hostname checking. Which call accomplishes this?

Accepted Answer

requests.get(url, verify='corp-ca.pem'). The verify parameter accepts either a boolean or a path to a CA bundle. Supplying the path to the corporate root certificate causes requests to trust that CA in addition to performing the usual certificate chain and hostname validation. Disabling verification, configuring a client certificate, or setting a proxy does not achieve trusted validation against a private CA.

Answer

requests.get(url, verify=False)

Answer

requests.get(url, proxies={'https': 'corp-ca.pem'})

Answer

requests.get(url, cert='corp-ca.pem')