New submission from Martijn Pieters:
The `BINARY_MODULO` operator hardcodes a test for `PyUnicode`:
TARGET(BINARY_MODULO) {
PyObject *divisor = POP();
PyObject *dividend = TOP();
PyObject *res = PyUnicode_CheckExact(dividend) ?
PyUnicode_Format(dividend, divisor) :
PyNumber_Remainder(dividend, divisor);
This means that a RHS subclass of str can't override the operator:
>>> class Foo(str):
... def __rmod__(self, other):
... return self % other
...
>>> "Bar: %s" % Foo("Foo: %s")
'Bar: Foo %s'
The expected output there is "Foo: Bar %s".
This works correctly for `bytes`:
>>> class FooBytes(bytes):
... def __rmod__(self, other):
... return self % other
...
>>> b"Bar: %s" % FooBytes(b"Foo: %s")
b'Foo: Bar: %s'
and for all other types where the RHS is a subclass.
Perhaps there should be a test to see if `divisor` is a subclass, and in that
case take the slow path?
----------
components: Interpreter Core
messages: 279993
nosy: mjpieters
priority: normal
severity: normal
status: open
title: RHS not consulted in `str % subclass_of_str` case.
type: behavior
versions: Python 2.7, Python 3.3, Python 3.4, Python 3.5, Python 3.6
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue28598>
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