I just came across a very strange line of code in Python:
....
self.myReturnCode = externalProcessPopen.returncode
....
....
return not self.myReturnCode
....
What exactly return not
stands for? I am aware that the returncode of a Popen process is None while it's still running and a random number once it completes and exits successfully. But what exactly is the author of the code trying to achieve here?
It might also be worth noting that the same author later on checks the return code like this:
if not testClass.testFunction():
logger.error('Failed to execute Function')
....
not
is a boolean operator that returns the boolean inverse of the value.return
returns the result of that operator. In other words, the expression should be read asreturn (not self.myReturnCode)
. Quoting the documentation:If
self.myReturnCode
is a true value,not self.myReturnCode
isFalse
, and vice versa. Note thatself.myReturnCode
can be any Python value, butnot
always returns a boolean value, eitherTrue
orFalse
.If
externalProcessPopen.returncode
is the return code of an external process, then it'll be a positive integer if the process exited with an error,0
if it exited successfully. This is called the process exit status; what non-zero values are returned depends entirely on the process.not 0
is thenTrue
,not 1
(or a higher integer value) gives youFalse
.If it is
None
, thenTrue
(not None
isTrue
) would be returned as well, but asubprocess.Popen()
return code is onlyNone
if the process has not yet exited.