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Why is the interpreter is returning a 'reference'?

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  Why is the interpreter is returning a 'reference'? Nir <nirchernia@gmail.com> - 2014-02-17 09:00 -0800
    Re: Why is the interpreter is returning a 'reference'? emile <emile@fenx.com> - 2014-02-17 09:08 -0800
    Re: Why is the interpreter is returning a 'reference'? Joel Goldstick <joel.goldstick@gmail.com> - 2014-02-17 12:08 -0500
    Re: Why is the interpreter is returning a 'reference'? Ned Batchelder <ned@nedbatchelder.com> - 2014-02-17 12:08 -0500
    Re: Why is the interpreter is returning a 'reference'? Marko Rauhamaa <marko@pacujo.net> - 2014-02-17 19:09 +0200
    Re: Why is the interpreter is returning a 'reference'? Zachary Ware <zachary.ware+pylist@gmail.com> - 2014-02-17 11:14 -0600
    Re: Why is the interpreter is returning a 'reference'? John Gordon <gordon@panix.com> - 2014-02-17 19:17 +0000

#66608 — Why is the interpreter is returning a 'reference'?

>>> k = ['hi','boss']
>>>
>>> k
['hi', 'boss']
>>> k= [s.upper for s in k]
>>> k
[<built-in method upper of str object at 0x00000000021B2AF8>, <built-in method upper of str object at 0x0000000002283F58>]

Why doesn't the python interpreter just return
['HI, 'BOSS'] ?

This isn't a big deal, but I am just curious as to why it does this.

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#66609

On 02/17/2014 09:00 AM, Nir wrote:
>>>> k = ['hi','boss']
>>>>
>>>> k
> ['hi', 'boss']
>>>> k= [s.upper for s in k]

s.upper is a reference to the method upper of s -- to execute the method 
add parens -- s.upper()

Emile


>>>> k
> [<built-in method upper of str object at 0x00000000021B2AF8>, <built-in method upper of str object at 0x0000000002283F58>]
>
> Why doesn't the python interpreter just return
> ['HI, 'BOSS'] ?
>
> This isn't a big deal, but I am just curious as to why it does this.
>

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#66610

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On Feb 17, 2014 12:05 PM, "Nir" <nirchernia@gmail.com> wrote:
>
> >>> k = ['hi','boss']
> >>>
> >>> k
> ['hi', 'boss']
> >>> k= [s.upper for s in k
S.upper()
> >>> k
> [<built-in method upper of str object at 0x00000000021B2AF8>, <built-in
method upper of str object at 0x0000000002283F58>]
>
> Why doesn't the python interpreter just return
> ['HI, 'BOSS'] ?
>
> This isn't a big deal, but I am just curious as to why it does this.
> --
> https://mail.python.org/mailman/listinfo/python-list

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#66611

On 2/17/14 12:00 PM, Nir wrote:
>>>> k = ['hi','boss']
>>>>
>>>> k
> ['hi', 'boss']
>>>> k= [s.upper for s in k]
>>>> k
> [<built-in method upper of str object at 0x00000000021B2AF8>, <built-in method upper of str object at 0x0000000002283F58>]
>
> Why doesn't the python interpreter just return
> ['HI, 'BOSS'] ?
>
> This isn't a big deal, but I am just curious as to why it does this.
>

You have to invoke s.upper, with parens:

     k = [s.upper() for s in k]

In Python, a function or method is a first-class object, so "s.upper" is 
a reference to the method, "s.upper()" is the result of calling the method.

-- 
Ned Batchelder, http://nedbatchelder.com

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#66612

Nir <nirchernia@gmail.com>:

>>>> k= [s.upper for s in k]
>>>> k
> [<built-in method upper of str object at 0x00000000021B2AF8>, <built-in method upper of str object at 0x0000000002283F58>]
>
> Why doesn't the python interpreter just return
> ['HI, 'BOSS'] ?

Try:

   k = [ s.upper() for s in k ]


Marko

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#66613

On Mon, Feb 17, 2014 at 11:00 AM, Nir <nirchernia@gmail.com> wrote:
>>>> k = ['hi','boss']
>>>>
>>>> k
> ['hi', 'boss']
>>>> k= [s.upper for s in k]
>>>> k
> [<built-in method upper of str object at 0x00000000021B2AF8>, <built-in method upper of str object at 0x0000000002283F58>]
>
> Why doesn't the python interpreter just return
> ['HI, 'BOSS'] ?

It's just doing exactly what you are telling it to :).  Your list
comprehension is constructing a list consisting of the 'upper' method
(which are themselves objects, able to be passed around just like any
other value) for each string object in list 'k'.  Consider this:

   >>> k = ['hi', 'boss']
   >>> s = k[0]
   >>> s
   'hi'
   >>> s.upper  # this just accesses the 'upper' attribute of 's',
which turns out to be its 'upper' method
   <built-in method upper of str object at 0xdeadbeef>
   >>> s.upper() # this actually calls the 'upper' method on 's'
   'HI'

Change your comprehension to actually call the upper method like so:
"k = [s.upper() for s in k]".  It will do what you expected with that
change.

Hope this helps,

-- 
Zach

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#66621

In <9b80c233-ad31-44c8-8a6e-9002ab11bd0d@googlegroups.com> Nir <nirchernia@gmail.com> writes:

> >>> k = ['hi','boss']
> >>>
> >>> k
> ['hi', 'boss']
> >>> k= [s.upper for s in k]
> >>> k
> [<built-in method upper of str object at 0x00000000021B2AF8>, <built-in method upper of str object at 0x0000000002283F58>]

> Why doesn't the python interpreter just return
> ['HI, 'BOSS'] ?

> This isn't a big deal, but I am just curious as to why it does this.

Because you typed 'str.upper' instead of 'str.upper()'.

-- 
John Gordon         Imagine what it must be like for a real medical doctor to
gordon@panix.com    watch 'House', or a real serial killer to watch 'Dexter'.

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