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List:       pykde
Subject:    Re: [PyQt] Where is the "<<" insertion overload done?
From:       Dmitry Shachnev <mitya57 () ubuntu ! com>
Date:       2014-11-25 6:48:30
Message-ID: CAKimPHU_mYspNboJE2Pbc2ps6BPyM6mtye+398zr5fXeH=3x4A () mail ! gmail ! com
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Hi,

On Tue, Nov 25, 2014 at 8:17 AM, David Cortesi <davecortesi@gmail.com> wrote:
> I've been happily using the "<<" insertion operator to write to QTextStreams
> for some time now, and only recently realized that "<<" is binary shift left
> in standard Python. Well, not so much realized, as had it rubbed in my face
> by PyLint, which warns that "stream << string" is an expression whose value
> is not being assigned.
>
> Somehow a QTextStream (derived) object arranges an overloaded meaning of
> ".write()" onto this operator. But where/how is the overload done?

Just like any other operator overload. Search for 'lshift_slot' in sip code.

Simple example code (in Python) if you want to do this yourself is attached.

--
Dmitry Shachnev

["test.py" (text/x-python)]

#!/usr/bin/env python3

class Printer:
    def __lshift__(self, value):
        print(value, end='')
        return self

    def __del__(self):
        print()

if __name__ == '__main__':
    Printer() << 'mitya' << 57

[Attachment #4 (text/plain)]

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