Is short-circuiting in assignment statements considered good style?

Question

If I understand correctly

myvar = a and b or c

gives the same result as

if a:
  if b:
    myvar = b
  else:
    myvar = c
else:
  myvar = c

so I guess it's more elegant.

I seem to remember seeing this kind of short-circuit assignment statement in JavaScript code. But is it considered good style in Python to use short-circuiting in assignment statements?

Answer 1

Most of the time, you then want to use a conditional expression instead:

myvar = b if a else c

Short-circuiting is very Pythonic however, just be aware of the pitfalls where b is false-y; using short-circuiting will result in different result in that case. Most of the time, you do not want to assign c instead.

Even in that case, you can still get the same result with an adjusted condition:

myvar = b if a and b else c

Short-circuiting is great for defaults:

foo = somevar or 'bar'

or for making sure pre-conditions are met:

foo = somevar and function_raises_exception_if_passed_empty_value(somevar)

Answer 2

This is really an opinion question, but for the most part, the answer is no. It goes against multiple style guides, probably because people tend to think it means "if a is true, use the value of b, otherwise use the value of c" rather than the real meaning, which is what you posted.

You probably want the new-ish conditional expression syntax instead:

myvar = b if a else c