Question 1

Compare compression algorithms: Gzip vs Snappy.

Accepted Answer

**Gzip:** Higher ratio (2–3x), slower (CPU). **Snappy:** Faster compress/decompress, lower ratio. **When:** Gzip cold storage/archival; Snappy hot/Spark. **Parquet:** Snappy default; good balance. **Why:** Match to workload. **Trade-off:** Zstd for better ratio + speed....

Question 2

Create a dictionary with list elements as keys and their occurrences as values.

Accepted Answer

**Code:** `Counter(lst)` or `{x: lst.count(x) for x in set(lst)}`. **Counter** optimized. O(n). **Why:** Frequency analysis. **Production:** Counter for most cases.

Question 3

Explain Lambda functions in Python.

Accepted Answer

**Lambda:** Anonymous single-expression. `lambda x: x*2`. **Use:** `sorted(key=lambda x: x[1])`, map, filter. **Limit:** One expression. **Why:** Inline; avoid def for one-offs. **Production:** Name for reuse; lambda for simple keys....

Question 4

Explain this code: [f(2) for f in [lambda x: x * i for i in range(5)]].

Accepted Answer

**Gotcha:** Lambdas close over i by reference. At execution, i=4. So each f(2)=2*4=8. **Result:** [8,8,8,8,8]. **Fix:** `lambda x, i=i: x*i` binds at creation. **Why:** Late binding. **Production:** Classic closure bug.

Question 5

Write a swap function without if-else.

Accepted Answer

**Python:** a, b = b, a (idiomatic). **XOR:** a^=b; b^=a; a^=b (integers). **Arithmetic:** a=a+b; b=a-b; a=a-b (overflow risk). Conditional swap: (a,b) if cond else (b,a)—expression, not if-else stmt.

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Gartner Python Interview Questions

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