En Sat, 31 Jan 2009 09:51:35 -0200, Csaba Hoch <csaba.h...@gmail.com>
escribió:
if I write the following:
>>> 1+1
2
it seems to be exactly equivalent to this:
>>> (1).__add__(1)
2
However, if I write invalid code and try to add a list to an int, the
errors will be different:
>>> 1+[]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for +: 'int' and 'list'
>>> (1).__add__([])
NotImplemented
I found that operator.__add__(1, []) gives the same result as 1+[].
What is the reason behind this difference between the __add__ operator
and int.__add__?
The operator "+" does more than blindy calling left.__add__(right). In
this case, as int + list returns NotImplemented, it reverses the operands
and tries right.__radd__(left), and only then it gives up and raises
TypeError.
The actual rules are a bit more complex, involving type conversion too;
see http://docs.python.org/reference/datamodel.html#emulating-numeric-types
--
Gabriel Genellina
--
http://mail.python.org/mailman/listinfo/python-list
