Module 01 — Interview Prep: Fundamentals

Setup, syntax, types, operators, I/O, control flow

Theory Questions

Q1: Is Python interpreted or compiled?
Both. Source → bytecode (.pyc) → PVM executes bytecode. "Interpreted" means no ahead-of-time machine code compilation.

Q2: Difference between == and is?
== compares values. is compares object identity (same memory address). Use is only for None, True, False.

Q3: List all falsy values.
None, False, 0, 0.0, "", [], {}, set(), (), range(0). Custom objects with __bool__ or __len__ returning False/0.

Q4: Mutable vs immutable types?
Mutable: list, dict, set, bytearray. Immutable: int, float, str, tuple, frozenset, bytes. Immutable objects are hashable (if contents hashable).

Q5: What is dynamic typing?
Variable types are determined at runtime. No need to declare type before assignment. Same variable can be reassigned to different types.

Q6: Why use virtual environments?
Isolate project dependencies. Avoid version conflicts between projects. Standard in all professional Python work.

Q7: python vs python3?
On macOS/Linux, python3 explicitly runs Python 3. Inside a venv, python points to the venv interpreter.

Q8: What is None?
Singleton representing absence of value. Type: NoneType. Always check with is None, never == None.

Q9: Difference between str and bytes?
str = Unicode text. bytes = raw binary. Encode: str → bytes. Decode: bytes → str.

Q10: What is the walrus operator :=?
Assigns and returns value in one expression (Python 3.8+). Example: if (n := len(data)) > 10:

Q11: break vs continue vs pass?
break exits loop. continue skips to next iteration. pass is a no-op placeholder.

Q12: When use for vs while?
for when iterating a known sequence. while when iterations depend on a condition.

Q13: What is match/case?
Structural pattern matching (Python 3.10+). Cleaner alternative to long if/elif chains.

Q14: Integer caching in Python?
Small integers (-5 to 256) may be cached. 256 is 256 often True; 257 is 257 may be False.

Q15: What is PEP 8?
Python style guide: snake_case functions, PascalCase classes, 4-space indent, max line length ~79-88.

Q16: What is __name__ == "__main__"?
Code runs only when file is executed directly, not when imported.

Q17: Short-circuit evaluation?
and/or stop evaluating once result is determined. False and expensive() never calls expensive().

Q18: Difference between / and //?
/ true division (float). // floor division (truncates toward negative infinity).

Q19: What is a docstring?
Triple-quoted string at top of module/function/class. Access via .__doc__. Used for documentation.

Q20: What is pip freeze?
Outputs installed packages with versions. Used to create requirements.txt.

Coding Questions

Q21: Swap two variables without temp

a, b = b, a

Q22: Check if number is even

def is_even(n: int) -> bool:
    return n % 2 == 0

Q23: FizzBuzz

for i in range(1, 101):
    if i % 15 == 0: print("FizzBuzz")
    elif i % 3 == 0: print("Fizz")
    elif i % 5 == 0: print("Buzz")
    else: print(i)

Q24: Check prime number

def is_prime(n: int) -> bool:
    if n < 2: return False
    for i in range(2, int(n ** 0.5) + 1):
        if n % i == 0: return False
    return True

Q25: Safe int conversion

def safe_int(s: str) -> int | None:
    try:
        return int(s)
    except ValueError:
        return None

Q26: Count vowels in string

def count_vowels(s: str) -> int:
    return sum(1 for c in s.lower() if c in "aeiou")

Q27: Reverse a string

s[::-1]

Q28: Find max without built-in max()

def find_max(nums):
    m = nums[0]
    for n in nums[1:]:
        if n > m: m = n
    return m

Common Pitfalls

Using is to compare strings or integers
== None instead of is None
Off-by-one errors with range()
Infinite while loops without update
Forgetting Python uses indentation, not braces
Installing packages globally instead of in venv

Quick Checklist

Explain == vs is with example
List all falsy values
Explain venv workflow end-to-end
Write FizzBuzz from memory
Explain match/case with example

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