POC Data Structures & File Handling 2

Question 1

What does the `collections.deque` class offer that a regular list does not?

Accepted Answer

O(1) append and pop from both ends

Answer

`deque` provides O(1) time complexity for appending and popping from both the left and right ends, while list pop(0) is O(n).

Question 2

Which file mode string opens a binary file for both reading and writing without truncating it?

Accepted Answer

rb+

Answer

`rb+` opens a binary file for both reading and writing, preserving existing content, while `wb` truncates the file.

Question 3

Given `d = {'a': 1, 'b': 2}`, what does `d.get('c', 0)` return?

Accepted Answer

0

Answer

`dict.get(key, default)` returns the default value (0 here) when the key is not found, instead of raising KeyError.

Question 4

What is the result of `[1, 2, 3] + [4, 5]` in Python?

Accepted Answer

[1, 2, 3, 4, 5]

Answer

The `+` operator on lists performs concatenation, returning a new list with all elements from both lists.

Question 5

When using `with open('file.txt') as f:`, what happens to the file when the block exits?

Accepted Answer

It is automatically closed

Answer

The context manager protocol calls `f.__exit__()`, which closes the file automatically even if an exception occurs.

(POC) Python Online Certification Practice Test