Python Interview Questions and Answers
Prepare for Python interviews with clear answers on data types, functions, generators, decorators, exceptions, OOP, testing and performance.
Strong Python interview answers explain the language behavior, the trade-off and a practical example. These questions cover the fundamentals most developers should be ready to discuss.
Python fundamentals interview questions
1. What is the difference between a list and a tuple?
Lists are mutable; tuples are immutable. Both preserve order and can hold mixed objects. Use a tuple for a fixed record or as a dictionary key when all elements are hashable.
2. What are mutable default arguments?
A default value is created once when the function is defined. Reusing a list or dictionary default can leak state between calls. Use None, then create the object inside the function.
3. What is the difference between == and is?
== compares values; is checks object identity. Use is None for the singleton None.
Functions, iterators and decorators
4. What do *args and **kwargs do?
They collect extra positional and keyword arguments. The same operators unpack iterables and mappings when calling a function.
5. What is a generator?
A generator yields values lazily, preserving its execution state between iterations. It can reduce memory use when processing a stream, but it is normally consumed once.
6. What is a decorator?
A decorator receives a function or class and returns a replacement. It is commonly used for logging, registration, caching and authorization. Use functools.wraps when wrapping functions.
OOP, exceptions and concurrency
7. Instance, class and static methods?
Instance methods receive self; class methods receive cls and often implement alternate constructors; static methods are namespaced utility functions with no automatic instance or class argument.
8. How should exceptions be handled?
Catch the narrowest expected exception, add useful context and avoid silently swallowing failures. Use finally or a context manager for cleanup.
9. What is the GIL?
In the traditional CPython build, the Global Interpreter Lock allows one thread to execute Python bytecode at a time. Threads still help I/O-bound work; processes or native extensions can help CPU-bound work. Confirm behavior for the Python build being discussed.
How to answer the coding portion
Clarify inputs, edge cases and complexity before coding. Write a small correct version, name variables clearly and test empty, single-item and invalid inputs. Explain time and space complexity and any library behavior your solution relies on.
Frequently asked questions
How many Python questions should I prepare?
Prepare concepts rather than memorizing a fixed number. Be ready to explain behavior and write small examples.
Should I use built-in functions in an interview?
Usually yes, unless the interviewer asks you to implement the underlying algorithm. Explain the complexity and trade-off.
Sources and further reading
Features, software and prices change. Confirm current details with these sources before making a decision.
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