Path: csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail
From: Peter Otten <__peter__@web.de>
Newsgroups: comp.lang.python
Subject: Re: Operator precedence problem
Date: Sun, 05 Jun 2016 09:35:44 +0200
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Xref: csiph.com comp.lang.python:109502

ICT Ezy wrote:

>>>> 2 ** 3 ** 2
> Answer is 512
> Why not 64?
> Order is right-left or left-right?

** is a special case:

"""
The power operator ** binds less tightly than an arithmetic or bitwise unary 
operator on its right, that is, 2**-1 is 0.5.
"""
https://docs.python.org/3.5/reference/expressions.html#id21

Here's a little demo:

$ cat arithdemo.py
class A:
    def __init__(self, value):
        self.value = str(value)
    def __add__(self, other):
        return self._op(other, "+")
    def __pow__(self, other):
        return self._op(other, "**")
    def __repr__(self):
        return self.value
    def _op(self, other, op):
        return A("({} {} {})".format(self.value, op, other.value))
$ python3 -i arithdemo.py 
>>> A(1) + A(2) + A(3)
((1 + 2) + 3)
>>> A(1) ** A(2) ** A(3)
(1 ** (2 ** 3))