Python | Intermediate | Priority

Question 1

How to sort a dictionary by values in descending order.

Answer 1

[(k, d[k]) for k in sorted(d, key=d.get, reverse=True)]
sorted(d.items(), key=itemgetter(1), reverse=True)
sorted(d.items(), key=lambda x: x[1], reverse=True)
# To keep using as a dictionary, wrap in an OrderedDict:
OrderedDict(sorted(…))

Ref Ref

Question 2

Example of how to make a class a contect manager?

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Answer 2

(See source material.)

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Question 3

What does a double leading underscore like “__var” do?

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Answer 3

Triggers name mangling when used in a class context. Enforced by the Python interpreter.

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Question 4

How to create a factory function?

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Answer 4

Define an inner function that returns a function.

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Question 5

What are (lexical) closures?

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Answer 5

Functions can be nested and they can capture and carry some of the parent function’s state with them. Functions that do this are called closures.

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Question 6

What’s a one-sentence definition of a decorator? In what order are decorators applied?

Answer 6

A decorator is a callable that takes a callable as input and returns another callable. Bottom to top.

Python Tricks 3.3 The Power of Decorators

Question 7

Putting a * before an iterable in a function call will do what? Putting a **?

Answer 7

Unpack it and pass its elements as separate positional arguments to the called function. Unpacks by matching up dictionary values and function arguments based on the dictionary keys.

Python Tricks 3.5 Function Argument Unpacking