PCPP1 Practice Exam 4 — 20 Questions

Question 1

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.

Answer

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

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

Answer

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

Question 2

You are developing a Tkinter application that includes a Canvas widget for drawing a dynamic bar chart. The chart data updates every second, and you must redraw the bars. To avoid visual flicker and improve performance, you decide to reuse existing canvas items instead of deleting and recreating them. Which Canvas method should you use to change the height of an existing rectangle item identified by its item ID?

Accepted Answer

canvas.coords(item_id, x1, y1, x2, y2). To dynamically update the size of an existing canvas item, you should modify its coordinates. The coords() method allows you to set new coordinates for an item, effectively resizing or repositioning it without deleting and recreating. This is efficient and avoids flicker. Other methods like itemconfig() are for changing options like fill, move() only translates, and scale() applies proportional scaling, which is not ideal for precise height adjustments.

Answer

canvas.move(item_id, 0, delta_y)

Answer

canvas.scale(item_id, x_origin, y_origin, x_scale, y_scale)

Answer

canvas.itemconfig(item_id, height=new_height)

Question 3

Which magic method is triggered when an object is deleted using the 'del' keyword?

Accepted Answer

__del__. The __del__ method is called when the object's reference count reaches zero.

Answer

__clear__

Answer

__remove__

Answer

__destroy__

Question 4

Which method is used to customize the behavior of the 'in' operator?

Accepted Answer

__contains__. The __contains__ method is called when using the 'in' or 'not in' operators.

Answer

__has__

Answer

__find__

Answer

__in__

Question 5

When using the __call__ method to implement a decorator, what does the decorator receive as an argument?

Accepted Answer

The function to be decorated.. The decorator receives the function object that is being decorated as the argument to the constructor (if the decorator is a class instance) or directly if it is a function.

Answer

The arguments to the function.

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The instance of the class.

Answer

The class object.

Question 6

How do you correctly call a method from a sibling class in a diamond inheritance structure using super()?

Accepted Answer

Use super() in each class to delegate to the next class in the MRO.. super() follows the Method Resolution Order (MRO), which correctly handles diamond inheritance by delegating calls to the next class in the chain, not just the parent.

Answer

Call the grandparent class directly.

Answer

Use the __bases__ attribute to iterate through parents.

Answer

Explicitly call the sibling class method by name.

Question 7

Which magic method is responsible for providing the informal string representation of an object, typically used for user-facing output?

Accepted Answer

__str__. The __str__ method is used for informal, readable string representations, whereas __repr__ is for formal, unambiguous representations.

Answer

__format__

Answer

__unicode__

Answer

__repr__

Question 8

Why does the 'abc' module provide the 'ABCMeta' metaclass?

Accepted Answer

To enforce abstract method implementation at instantiation.. ABCMeta is the metaclass that implements the logic to prevent instantiation of classes with abstract methods.

Answer

To allow private methods.

Answer

To improve method resolution speed.

Answer

To support multiple inheritance.

Question 9

Which magic method enables index access (e.g., obj[i])?

Accepted Answer

__getitem__. The __getitem__ method allows an object to support indexing.

Answer

__index__

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__setitem__

Answer

__access__

Question 10

When naming a constant in Python, which convention does PEP 8 recommend?

Accepted Answer

UPPER_CASE_WITH_UNDERSCORES.. Constants should be named using all capital letters with underscores to separate words.

Answer

PascalCase.

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snake_case.

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CamelCase.

Question 11

Which magic method should you implement to make your objects support the 'with' statement context manager?

Accepted Answer

__enter__ and __exit__. The __enter__ and __exit__ methods are required to implement the context manager protocol.

Answer

__context__

Answer

__open__ and __close__

Answer

__init__ and __del__

Question 12

According to PEP 257, what is the standard format for a single-line docstring?

Accepted Answer

Use triple quotes and keep the summary on the same line, ending with a period.. A single-line docstring should be on the same line as the opening triple quotes, ending with a period.

Answer

Use a single quote for the entire block.

Answer

The docstring should span three lines including the summary.

Answer

The summary should start on the next line.

Question 13

You are building a REST client that needs to handle 429 Too Many Requests status codes. Which strategy is most effective when implementing an automatic retry mechanism?

Accepted Answer

Implement an exponential backoff strategy with jitter. Implementing exponential backoff ensures that you do not overwhelm the server while waiting for the rate limit to reset.

Answer

Switch to a different base URL immediately

Answer

Ignore 429 errors and continue execution

Answer

Retry immediately in a loop until successful

Question 14

Which magic method is used to control how an instance is displayed when using the print() function?

Accepted Answer

__str__. print() implicitly calls str(obj), which in turn calls __str__.

Answer

__display__

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__repr__

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__print__

Question 15

You are writing to a CSV file. If your data contains the delimiter character itself (e.g., a comma in a text field), what does the csv module do by default?

Accepted Answer

It quotes the field.. The csv module automatically wraps such fields in quotes.

Answer

It raises a csv.Error.

Answer

It ignores the delimiter.

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It escapes the character with a backslash.

Question 16

When using configparser, how do you handle multiline values?

Accepted Answer

Indent the subsequent lines.. You indent lines following the initial line within the option.

Answer

Use a backslash at the end of each line.

Answer

Wrap them in triple quotes ('''...''').

Answer

Use the '
' escape character.

Question 17

You are using sqlite3 and need to enforce foreign key constraints. How do you enable them?

Accepted Answer

connection.execute('PRAGMA foreign_keys = ON'). You must execute the command 'PRAGMA foreign_keys = ON;' on the connection.

Answer

It is enabled by default.

Answer

connection.execute('SET FOREIGN_KEYS ON')

Answer

connection.enable_foreign_keys()

Question 18

Which of the following headers is commonly used in REST APIs to indicate the format of the request body?

Accepted Answer

Content-Type. The 'Content-Type' header tells the server what type of media is being sent in the request body.

Answer

Authorization

Answer

Accept

Answer

User-Agent

Question 19

When sending a JSON payload with 'requests.post()', which argument should you use to automatically set the 'Content-Type' to 'application/json'?

Accepted Answer

json=payload. The 'json' argument automatically serializes the data and sets the correct headers.

Answer

data=json.dumps(payload)

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params=payload

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body=payload

Question 20

What is the primary risk of using 'getattr' without a default value?

Accepted Answer

It raises an AttributeError.. If the attribute is not found, it raises an AttributeError, potentially crashing the application if not handled.

Answer

It returns None.

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It enters an infinite loop.

Answer

It creates the attribute.