print stream behavior

Andreas Kraemer akraemer at sbcglobal.net
Wed May 27 20:02:55 CEST 2009


On May 27, 10:52 am, Peter Otten <__pete... at web.de> wrote:
> This is a longstanding quirk of the CPython implementation. The
> PRINT_ITEM_TO opcode triggers a PyFile_WriteObject() call which in turn does
> the C equivalent of
>
> if isinstance(f, file):
>    file.write(f, s)
> else:
>    write = getattr(f, "write")
>    write(s)
>
> Therefore subclasses of file will always use file.write() when invoked via
> 'print'.
>
> You can avoid that by writing a wrapper instead of a subclass:
>
> class File(object):
>     def __init__(self, *args):
>         self._file = open(*args)
>     def write(self, s):
>         self._file.write(s)
>     # add other methods as needed
>
> Peter

Thanks very much! That solves the mystery ...



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