Ahh, so it's a mutable thing. That makes sense that I can't change a mutable object and thus can't affect it outside of the function. Does that mean Python functions aren't always byref, but are sometimes byval for nonmutables?
-Greg On 8/9/05, Dennis Lee Bieber <[EMAIL PROTECTED]> wrote: > On Tue, 9 Aug 2005 10:53:15 -0400, Gregory Piñero <[EMAIL PROTECTED] > > declaimed the following in comp.lang.python: > > <rhetorical> Is this the third time this week that this has come > up? > > > Hey guys, would someone mind giving me a quick rundown of how > > references work in Python when passing arguments into functions? The > > code below should highlight my specific confusion: > > > They work just like they do everywhere else... > > Read the manuals on mutable and immutable objects. (I'd suggest > language reference chapter 3 and 4, library reference chapter 2.3.6, > 2.3.7) > > "names" in Python are movable labels attached to objects; they > are not fixed locations in memory to which object are copied; hence they > do not behave like variables in traditional languages. > > > > > bool1=True > > immutable object -- "bool1" is a label attached to a fixed > object > > > lst1=[1,2,3] > > > mutable object -- "lst1" is a label attached to a box > containing objects > > > def func1(arg1): arg1.append(4) > > > > "arg1" is a label attached to whatever object was passed in... > .append is an operation that changes what is /inside/ that > object > > > def func2(arg1): arg1=False > > > "arg1" is a label attached to whatever was passed in... > Assignment (especially of an immutable object) takes that label > OFF of the object that was passed in, and moves it the object of the > assignment. It does not move the label that is outside the call. > > > >>func1(lst1) > > >>lst1 > > [1,2,3,4] > > > "lst1" is the label of the box; inside of func1, that box has > two labels: "lst1" and "arg1". You used the "arg1" label to locate the > box, and then you changed what was inside the box. Outside the function, > you used the "lst1" label to find the /same/ box and report what was > inside it. > > > >>func2(bool1) > > >>bool1 > > True > > > "bool1" is the label of a non-box -- a "true". Inside the > function "true" has initially two labels: "bool1" and "arg1". You then > moved the "arg1" label from "true" to a different object "false". > "bool1" does not move, and still references the "true". > > > -- > > ============================================================== < > > [EMAIL PROTECTED] | Wulfraed Dennis Lee Bieber KD6MOG < > > [EMAIL PROTECTED] | Bestiaria Support Staff < > > ============================================================== < > > Home Page: <http://www.dm.net/~wulfraed/ > < > > Overflow Page: <http://wlfraed.home.netcom.com/ > < > -- > http://mail.python.org/mailman/listinfo/python-list > -- Gregory Piñero Chief Innovation Officer Blended Technologies (www.blendedtechnologies.com) -- http://mail.python.org/mailman/listinfo/python-list
