A certainl part of an if() structure never gets executed.
R. Michael Weylandt
michael.weylandt at gmail.com
Sun Jun 16 06:42:36 EDT 2013
On Sun, Jun 16, 2013 at 10:59 AM, Nick the Gr33k <support at superhost.gr> wrote:
> On 16/6/2013 12:22 μμ, Denis McMahon wrote:
>>
>> For example, in Python
>>
>> a = 6
>> b = a
>> c = 6
>>
>> a and b point to one memory location that contains the value 6
>> c points to a different memory location that contains the value 6
>
>
> I believe you are mistaken.
>
> a here is not a pointer but variable,
> which is a memory location that stores value 6.
>
> b here is a pointer. It's value is the memory location of variable a which
> stores value 6.
>
> c here is just te same as a , a variable.
Actually, y'all both might be. This is a bit CPython specific and not
mandated by the language specification.
To Nikos: please don't extrapolate from the examples below. They are a
CPython (the most common implementation of the Python language)
specific detail.
## CODE SNIPPET##
a = 6; b = a; c = 6
id(a)
id(b)
id(c)
## END CODE##
These are all the same, indicating that they all point to the "same 6"
in memory. That's a CPython specific optimization (caching small
integers) which is not guaranteed by the language and changes between
pythons and between compiles.
For example,
## CODE SNIPPET##
a = 552315251254
b = a
c = 552315251254
a is b # True _on my machine_
a is c # False _on my machine_
id(a)
id(b)
id(c)
## END CODE##
Note that to compare if two names point to the same "object, you can
use the "is" operator.
a is b
c is a
etc.
>
>>> A pointer = a variable that has as a value a memory address a variable =
>>> a memory address that has as a value the actual value we want to store.
>>
>>
>> These are really C terms, not Python terms. Stop thinking that C is
>> behaving like Python.
>
>
>
> I think it behaves the same way, but lets here from someone else too.
I understand the Greeks invented democracy and all that, but facts
aren't subject to it.
>
> Whats the difference of "interpreting " to "compiling" ?
If only it could be googled.... Alas, no one has ever written anything
about technology on the internet. Ironic that...
Michael
More information about the Python-list
mailing list