Ian Kelly wrote: > On Sat, Dec 10, 2016 at 11:40 PM, Veek M <vek.m1...@gmail.com> wrote: >> Well take a look at this: >> ########################################### >> #!/usr/bin/python >> >> class Foo(int): >> def __init__(self, value): >> self.value = value >> >> def __str__(self): >> print '__str__' >> return str(self.value) >> >> def __int__(self): >> print '__int__' >> return self.value + 1 >> >> >> #'%s' % Foo(10) # %s is mapped to __str__ >> '%d' % Foo(20) >> ########################################### >> >> here, '__str__' prints because when you do: >> '%s' % x >> the __str__ method is invoked. So internally %s invokes __str__ >> independent of print. >> >> However the next line doesn't trigger any similar invocation with >> __int__ or__str__? (but int(Foo(10)) would invoked __int__) > > This is probably because Foo inherits from int. Foo(20) is already an > int so there is no conversion to be done; Python simply uses the int > value and ignores the __int__ method in this case. > >> Is there a way to trigger special methods using %d etc OR is this >> restricted to %s and why? > > For an object that is already an int, probably not. > > However you may want to revisit your decision to make Foo inherit from > int and question whether that is really sensible if you're also > wanting to override the __int__ method. What does that mean if > something is an int but also provides a method to convert to int? It's > a contradiction.
Ah! thanks guys, now it works great. (I still need to ponder all this anyhow but yay!) -- https://mail.python.org/mailman/listinfo/python-list
