Popen4 exception handling

[Jim]

Hi, I'm using popen2.Popen4 and I'm curious what exceptions it could
raise

for example
    p = popen2.POpen4( 'command string' )
i'm assuming would only raise OSError exceptions if something went
wrong internally with popen.

and also, for read operations like:
    p.fromchild.read()
i'm assuming it would raise IOError exceptions

is this correct? or maybe popen2 module does somethign else?
thanks