3 ms·

"not key in dct", or "not (key in dct)", is never slower than "key not in dct" because when key is found in dct, the expression is immediately true.

• andreasvc 14y ago
  Perhaps, but it reads oddly which is reason enough to avoid it.
• Nurdok 14y ago
  They are equivalent, but the latter version is more readable.
• pjscott 14y ago
  Those actually generate the same bytecode in Python 2.7. Probably other versions, as well.