Python Exponent Question

[databyss]

I have a simple program and the output isn't what I expect. Could
somebody please explain why?

Here's the code:

#simple program
print "v = 2"
v = 2
print "v**v = 2**2 =", v**v
print "v**v**v = 2**2**2 =", v**v**v
print "v**v**v**v = 2**2**2**2 =", v**v**v**v
#end program

Here's the output:
v = 2
v**v = 2**2 = 4
v**v**v = 2**2**2 = 16
v**v**v**v = 2**2**2**2 = 65536
I would expect 2**2**2**2 to be 256

 

[Carsten Haese]

I have a simple program and the output isn't what I expect. Could
somebody please explain why?
[...]
v**v**v**v = 2**2**2**2 = 65536

I would expect 2**2**2**2 to be 256

Exponentiation is right-associative. 2**2**2**2 = 2**(2**(2**2)) =
2**(2**4) = 2**16 = 65536.

 

[Zero Piraeus]

:

v = 2
v**v = 2**2 = 4
v**v**v = 2**2**2 = 16
v**v**v**v = 2**2**2**2 = 65536

I would expect 2**2**2**2 to be 256

"... in an unparenthesized sequence of power and unary operators, the
operators are evaluated from right to left ..."
- http://docs.python.org/ref/power.html

So, 2**2**2**2 = 2**(2**(2**2)) = 65536

-[]z.

 

[Robert Kern]

I have a simple program and the output isn't what I expect. Could
somebody please explain why?

Here's the code:

#simple program
print "v = 2"
v = 2
print "v**v = 2**2 =", v**v
print "v**v**v = 2**2**2 =", v**v**v
print "v**v**v**v = 2**2**2**2 =", v**v**v**v
#end program

Here's the output:

v = 2
v**v = 2**2 = 4
v**v**v = 2**2**2 = 16
v**v**v**v = 2**2**2**2 = 65536

I would expect 2**2**2**2 to be 256

Exponentiation is right-associative. I.e. 2**2**2**2 == 2**(2**(2**2))

The reason is that left-associativity is better written with multiplication.

(x**y)**z == x**(y*z)

--
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco

 

[Tim Chase]

I have a simple program and the output isn't what I expect. Could
somebody please explain why?

Here's the code:

#simple program
print "v = 2"
v = 2
print "v**v = 2**2 =", v**v
print "v**v**v = 2**2**2 =", v**v**v
print "v**v**v**v = 2**2**2**2 =", v**v**v**v
#end program

Here's the output:

v = 2
v**v = 2**2 = 4
v**v**v = 2**2**2 = 16
v**v**v**v = 2**2**2**2 = 65536

I would expect 2**2**2**2 to be 256

Order of operations and proximity:
256

Apparently Python assumes the former and you assume the latter.
When in doubt about order of operations, use parens. And even
when you *know* the order of operations, be kind to those who
will have to read your code later and put in the parens anyways.

-tkc

 

[Christian Heimes]

I would expect 2**2**2**2 to be 256

I stumbled upon it, too.

2**2**2**2 == 2**(2**(2**2)) == 2**16 == 65536

Christian

 

[Christian Heimes]

I would expect 2**2**2**2 to be 256

I stumbled upon it, too.

2**2**2**2 == 2**(2**(2**2)) == 2**16 == 65536

Christian

 

[Michael J. Fromberger]

I have a simple program and the output isn't what I expect. Could
somebody please explain why?

Here's the code:

#simple program
print "v = 2"
v = 2
print "v**v = 2**2 =", v**v
print "v**v**v = 2**2**2 =", v**v**v
print "v**v**v**v = 2**2**2**2 =", v**v**v**v
#end program

Here's the output:

v = 2
v**v = 2**2 = 4
v**v**v = 2**2**2 = 16
v**v**v**v = 2**2**2**2 = 65536

I would expect 2**2**2**2 to be 256

Python's ** operator associates to the right, not to the left; thus,

2 ** 2 ** 2 ** 2

.... really means

2 ** (2 ** (2 ** 2))

.... and not

((2 ** 2) ** 2) ** 2

.... as you seem to expect. As usual, you can enforce different
associations by explicitly including the parentheses.

Cheers,
-M