Python Interview Prep - Programming

A default argument like def f(items=[]) is evaluated once when the function is defined, so the same list is shared across every call that uses the default. Appending to it persists between calls, causing surprising bugs. The fix is to default to None and create a new list inside the function body.

Dictionaries and sets provide average O(1) lookups because they use hashing, while checking membership in a list is O(n). In interviews, converting a list to a set or using a dict to count frequencies often turns a slow nested loop into a fast single pass, which interviewers reward.

A shallow copy, from copy.copy or slicing, creates a new outer object but shares references to nested objects, so changing a nested list affects both copies. A deep copy, from copy.deepcopy, recursively duplicates everything, so the copies are fully independent. This distinction matters when mutating nested data in interview problems.

Both are valid, but Python has a default recursion limit near one thousand and no tail-call optimization, so deep recursion can raise RecursionError. For very deep problems an explicit stack or an iterative approach is safer. Mention this tradeoff aloud, since interviewers value candidates who understand Python's recursion constraints.

Use LeetCode and HackerRank to practice algorithm and data-structure problems in Python, starting with easy problems on arrays, strings, and hash maps before moving to trees, graphs, and dynamic programming. Focus on writing clean, correct solutions and analyzing time and space complexity. Revisit problems you missed and learn common patterns rather than memorizing individual answers.

Common questions cover the difference between lists and tuples, how dictionaries and sets work, comprehensions, generators, decorators, and the meaning of mutable versus immutable. A useful cheat sheet lists built-in data structures, string methods, slicing, and complexity of common operations. Also review exceptions, context managers, and how Python handles variable scope and default arguments.

Instead of one downloadable file, review the topics interviewers test. Know the built-in data structures and their time complexity, especially dict and set lookups. Understand mutability, shallow versus deep copy, comprehensions, generators, and the difference between == and is. Add decorators, context managers, and common idioms. Practice explaining trade-offs on LeetCode problems so the reasoning, not just the answer, comes easily.

There is no pass/fail threshold. The test measures your knowledge level and provides detailed feedback for improvement.

For knowledge tests, we recommend answering without external help to get an accurate assessment. Practice exercises are designed for learning, so references are acceptable.

Our questions are written for structured educational practice and can give a useful snapshot of your current knowledge in the tested topics.