Interview Q&A / Python

1. What does this function return when both try and finally have a return statement?

   It returns the value from the finally block. finally always runs last, and a return inside it overrides the earlier return and even discards a pending exception. This is why returning from finally is considered bad practice.

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2. What does this print: a list of lambdas created in a loop, each returning i?

   All the lambdas print the last value of i. Closures capture the variable, not its value at creation time, and i is looked up when the lambda is called. Fix it with a default argument: lambda i=i: i.

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3. What does yield from do in Python?

   yield from iterable hands over each item of another iterable or generator to the caller, as if you had written a for loop with yield. It also passes through values sent into the generator and returns the sub-generator's return value.

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4. What is a circular import in Python, and how do you fix it?

   A circular import happens when module A imports B while B imports A, so one of them is used before it is fully loaded, causing ImportError or AttributeError. Fix it by restructuring, moving the shared code to a third module, or importing inside the function.

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5. What is the Method Resolution Order (MRO) in Python, and how does it work with multiple inheritance?

   The MRO is the order in which Python searches a class and its parents for an attribute. It uses C3 linearization: children come before parents, and the order of bases you wrote is kept. You can see it with ClassName.__mro__ or mro().

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6. Why must you define __hash__ when you define __eq__ for objects used in sets or as dict keys?

   Objects that compare equal must have the same hash, or sets and dicts will treat them as different. Defining __eq__ without __hash__ sets __hash__ to None, so the class becomes unhashable. Base the hash on the same fields that __eq__ compares.

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