On 9/5/2013 12:37 PM, jsri...@gmail.com wrote:
I am going through the tutorials on docs.python.org, and I came across this
excerpt from http://docs.python.org/3/tutorial/controlflow.html:
"The execution of a function introduces a new symbol table used for the local
variables of the function. More precisely, all variable assignments in a function
store the value in the local symbol table; whereas variable references first look in
the local symbol table, then in the local symbol tables of enclosing functions, then
in the global symbol table, and finally in the table of built-in names. Thus, global
variables cannot be directly assigned a value within a function (unless named in a
global statement), although they may be referenced.
"The actual parameters (arguments) to a function call are introduced in the
local
symbol table of the called function when it is called; thus, arguments are
passed
using call by value (where the value is always an object reference, not the
value
of the object). [1] When a function calls another function, a new local symbol
table is created for that call."
Even as a professional programmer, I'm not really able to follow this. It
seems self-contradictory, amgiguous, and incomplete. The problem with looking
for this information elsewhere is that it's not going to be all in one spot
like this half the time, and it's not going to be readily searchable on Google
without more knowledge of what it's referring to. However this looks like
something that's too important to overlook.
The only incompleteness is that 'global statememt' should be 'global or
nonlocal statement'.
I can tell it's referring to things like scope, pass-by-value, references,
probably the call stack, etc., but it is written extremely poorly. Translation
please? Thanks!
Without knowing your personal language, translating into a language you
would understand is an impossible task. I would replace 'variable' with
'name', 'symbol table' with 'nmespace', 'call by object reference value'
with 'call by object', and 'global' with 'modular'. Maybe that helps
you, maybe it confuses you more.
The importance thing you must understand is that Python is an
object-based language and that calling a function (like assignment
statement in general) does not copy the argument objects.
I suggest that you study the behavior of actual examples both in the
tutorial and ones you make up. If you are actually baffled by some
behavior, ask a spedific question.
PS. Try not to double post.
--
Terry Jan Reedy
--
https://mail.python.org/mailman/listinfo/python-list
