Op 2005-01-14, Roel Schroeven schreef <[EMAIL PROTECTED]>:
Antoon Pardon wrote:
IMO we have a: dogs are mamals kind of relationship in Python.
I see what you mean, but I don't think it's true.
Every expression can be used where a statement is expected. (And this can be worded as: every expression is a statement.)
Not really. An expression statement is a statement that looks like an expression, but actually it's more than that: not only does it calculate the value of the expression, it also prints the value.
1) Only in an interactive environment.
True, I wanted to add that but forgot it. Doesn't change what I'm saying though.
2) That the semantics differ according to where the expression is
used doesn't make a difference. That an expression decides which
branch of an if statement is executed or what object is pass
as an argument in a call are also semantic difference, yet we still have an expression in both cases.
In both cases we have an expression, in both cases we have a statement, in both cases the expression is a part of the statement. In one case the expression is the only statement, in the other case the statement has other parts too.
Note that it would be perfectly possible to modify the syntax into
expression_stmt ::= "exprstmt" expression_list ...
If you change the syntax, of course you will change the strings that will be accepted. I could change the syntax to:
if_stmt ::= "if" "ifexpr" expression ...
Have I now proved that expressions after an if are not normal expressions?
No, you still have a statement with one or more parts, one of which is an expression.
In OOP terms: I think that an expression statement 'has an' expression (I agree that is a very thin wrapper though), not that an expression statement 'is an' expression.
Not every statement can be used where an expression is expected.
AFAIK *no* statement can be used where an expression is expected.
But that was not the implication of what Guido supposedly had said. So that this is not the case doesn't counter what I said.
Whether statements can be used in the place of expressions is indeed not relevant to the discussion.
Regarding what Guido apparently said:
Op 2005-01-12, Steve Holden schreef <[EMAIL PROTECTED]>: >> Given that Guido is on record as saying that expressions aren't >> statements because he wants those things to be separate
Antoon Pardon wrote: > Well, it seems that Guido is wrong then. The documentation clearly > states that an expression is a statement.
I don't think it says that at all.
> More specifically, everywhere you can use a statement, you can > simply use an expression according to the python syntax.
If you use an expression where a statement is expected, you really write an expression statement that contains the expression (and nothing else, but that doesn't matter).
-- "Codito ergo sum" Roel Schroeven -- http://mail.python.org/mailman/listinfo/python-list
