On 29-Nov-09 19:50 PM, Chris Rebert wrote:
On Sun, Nov 29, 2009 at 4:39 PM, Esmail<ebo...@hotmail.com> wrote:
Ok, this is somewhat unexpected:
Python 2.6.2 (release26-maint, Apr 19 2009, 01:56:41)
[GCC 4.3.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
-3**2
-9
x = -3
x**2
9
I would have expected the same result in both cases.
Initially I would have expected -3**2 to yield 9, but I can accept
that ** binds tighter than the unary -, but shouldn't the results
be consistent regardless if I use a literal or a variable?
_No_, because using the variable evaluates "-3" as a unit separately
by itself, before the exponentiation ever occurs; it's the same as the
difference between (-3)**2 and -3**2.
Python is not a concatenative programming language[*]; you can't
directly textually replace a variable with its value and expect to get
the same result from an expression. For instance, in this case, you
need to add the parentheses.
Cheers,
Chris
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[*] http://en.wikipedia.org/wiki/Concatenative_language
See the Operator Order of Precedence:
http://docs.python.org/reference/expressions.html#summary
Parentheses permit the user to vary the precedence.
Colin W.
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