overriding file.readline: "an integer is required"

[kj]

I'm trying to subclass file, overriding the readline method.  The
new method definition begins with

    def readline(self, size=None):
        line = self.file.readline(size)
        # etc., etc.

...where the self.file attribute is a regular file object.

This works fine if I invoke the new method with an integer argument,
but if I invoke it without arguments, I get the error

TypeError: an integer is required

...which I suppose comes from the call to self.file.readline(None).

I know that I could rewrite the method like this:

    def readline(self, size=None):
        if size == None:
            line = self.file.readline()
        else:
            line = self.file.readline(size)
        # etc., etc.

...but this seems to me exceptionally awkward.  (Actually, it's worse
than awkward: it fails to complain when the overriding method is
called with the argument None.  It would be better to test for the
number of arguments passed to the function, but I can't figure out
how to do this either.)

Is there a better idiom?

TIA!

Kynn
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