On 26/03/2016 23:30, John Pote wrote:
So intrigued by this question I tried the following
def fnc( n ):
print "fnc called with parameter '%d'" % n
return n
for i in range(0,5):
if i%2 == 0:
fnc
next
print i
and got the same result as the OP
A couple of tests showed that the only important thing about the name in
the if clause is that it is known at runtime and then it is silently
ignored.
However, if the name is not known/accessible at run time a 'NameError'
is raised,
NameError: name 'mynewfn123' is not defined
On the other hand the following if clause
if i%2 == 0:
fnc next
The results aren't surprising once you know what's going on.
If you have:
fnc
then this name is evaluated (it refers to a function object given your
definition. Then that value is discarded. But this:
kljgkjhgjk
is not defined anywhere, and it can't evaluate it, raising the name
error. While in:
fnc()
the 'fnc' is evaluated, and then it's called (when it should give a
parameter error as your def expects one). But
abc def
is just a syntax error as usually two identifiers can't be adjacent
(AFAIK) except where the first is a reserved word.
So I have sympathy with the OP, I would expect the compiler to pick this
up - indeed it does so for two (or more ?) unused names on a single
line. That is unless someone can give a useful use of this behaviour or
is there something going on under the Python hood I'm not aware of?
This one of those features I think that do have the odd use but most of
the time just result in perplexing results or hard-to-find bugs. It
could have been eliminated from the language (especially as many people
aren't even aware of the possibilities) with little loss.
Someone who desperately wants to evaluate a name or expression can
always use something like:
def test(x):pass
test(fnc)
for the same purpose. But this time it's obvious. (Ideally it would be a
built-in construct to avoid the call overhead.)
--
Bartc
--
https://mail.python.org/mailman/listinfo/python-list
