exception in child process propagates

The code, simplified, is:

def _spawn(self,command,args=[]):
    ...
    if self.pid == 0: # Child
        ...
        os.exec...(...)

If an exception occurs if this child section, e.g. exec fails or any of the other instructions, the propagation is passed upwards to the caller, which is confusing because this is not the process that called the function. i.e. two processes return when you only expect one process to return.

This can be fixed by changing the child code to exit on exception:

def _spawn(self,command,args=[]):
    ...
    if self.pid == 0: # Child
        try:
            ...
            os.exec...(...)
        finally:
             sys.exit(1)

Note I have used finally here as exec should never return. So finally will only get executed if something went wrong.

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