Python Interview Questions and Answers: Memory Management, Lambda, List Operations, Exceptions, and More

1. How does Python manage memory? Python uses three mechanisms: (a) reference counting – every object has a count of references; the count increases when a new name is bound or the object is placed in a container and decreases when references are deleted or go out of scope. The built‑in sys.getrefcount() can inspect the count. (b) garbage collection – when an object's reference count drops to zero it is reclaimed, and a cyclic‑gc detector periodically breaks reference cycles that would otherwise leak memory. (c) memory pool (pymalloc) – small objects (<256 bytes) are allocated from private pools for speed, while larger objects use the system malloc .

2. What is a lambda function and its benefits? A lambda is an anonymous, inline function useful for short callbacks. Syntax: lambda arguments: expression . Example:

add = lambda x, y: x + y
print(add(2, 3))  # 5

3. Converting between tuple and list – simply use the built‑in tuple() and list() constructors; type() can check the result.

4. Removing duplicate elements from a list – three common methods:

Method 1: use a set and restore original order.

info = [1, 2, 4, 1, 5, 6, 5, 0, 9, 0, 7, 7]
result = list(set(info))
result.sort(key=info.index)
print(result)

Method 2: use dict.fromkeys() to preserve order.

result = dict.fromkeys(info)
result_list = list(result.keys())
print(result_list)

Method 3: list comprehension.

lst = []
[ lst.append(i) for i in info if i not in lst ]
print(lst)

5. Sorting a list and processing from the last element – after list.sort() , iterate backwards with range(len(a)-2, -1, -1) and delete duplicates of the last element.

a.sort()
last = a[-1]
for i in range(len(a)-2, -1, -1):
    if last == a[i]:
        del a[i]
    else:
        last = a[i]
print(a)

6. Copying objects – assignment creates a new reference; shallow copy duplicates the container but keeps references to inner objects (e.g., copy.copy() or slicing); deep copy recursively copies everything ( copy.deepcopy() ).

7. Using except – the try…except…else…finally block catches specific exceptions, executes the else block only when no exception occurs, and always runs finally for cleanup.

8. The pass statement does nothing and serves as a placeholder where syntactically a statement is required.

9. The range() function creates an immutable sequence of integers: range(start, stop[, step]) . Example parameters are explained.

10. Searching and replacing strings – use the re module’s sub() (or subn() ) function.

import re
p = re.compile('蓝色|白色|红色')
print(p.sub('彩色', '蓝色袜子和红色鞋子'))
print(p.sub('彩色', '蓝色袜子和红色鞋子', count=1))

11. Difference between match() and search() – match() checks only at the start of the string, while search() scans the entire string for the first occurrence.

12. Generating random numbers – the random module provides random() , uniform(a,b) , randint(a,b) , randrange(a,b,step) , and choice(seq) for various random values.