procutil: ensure that procutil.std{out,err}.write() writes all bytes Python 3 offers different kind of streams and it’s not guaranteed for all of them that calling write() writes all bytes. When Python is started in unbuffered mode, sys.std{out,err}.buffer are instances of io.FileIO, whose write() can write less bytes for platform-specific reasons (e.g. Linux has a 0x7ffff000 bytes maximum and could write less if interrupted by a signal; when writing to Windows consoles, it’s limited to 32767 bytes to avoid the "not enough space" error). This can lead to silent loss of data, both when using sys.std{out,err}.buffer (which may in fact not be a buffered stream) and when using the text streams sys.std{out,err} (I’ve created a CPython bug report for that: https://bugs.python.org/issue41221). Python may fix the problem at some point. For now, we implement our own wrapper for procutil.std{out,err} that calls the raw stream’s write() method until all bytes have been written. We don’t use sys.std{out,err} for larger writes, so I think it’s not worth the effort to patch them.