Op 14/11/2022 om 4:23 schreef DFS:
On 11/13/2022 9:11 PM, Chris Angelico wrote:
On Mon, 14 Nov 2022 at 11:53, DFS <nos...@dfs.com> wrote:
On 11/13/2022 5:20 PM, Jon Ribbens wrote:
On 2022-11-13, DFS <nos...@dfs.com> wrote:
In code, list.clear is just ignored.
At the terminal, list.clear shows
<built-in method clear of list object at 0x000001C9CFEC4240>
in code:
x = [1,2,3]
x.clear
print(len(x))
3
But why is it allowed in the first place?
I stared at list.clear and surrounding code a dozen times and said
"Looks right! Why isn't it clearing the list?!?!"
2 parens later and I'm golden!
No part of it is invalid, so nothing causes a problem. For instance,
you can write this:
If it wastes time like that it's invalid.
It's not invalid. In the REPL for example, it does something useful:
>>> x = [1, 2, 3]
>>> x.clear
<built-in method clear of list object at 0x000002947DBBF680>
Others have shown instances where writing a method or function without
calling it are useful in a script too.
There are languages that handle this differently. Ruby, for example,
calls the function/method even when you don't write the parens, if I'm
not mistaken. Personally I don't like that; I much prefer Python's
explicitness in making the difference between the value of a function
and calling that function. Still, there's something to be said for
warnings. I agree with others that such warnings are more the job for a
linter than for the language.
FWIW I've been bitten by this in C++ once. I wanted to write something like
if (some_condition())
foo();
But I forgot the parens after some_condition, so C++ evaluated the
function pointer (which was non-NULL so evaluated is true in a boolean
context) instead of the return value, and therefore foo() got called
unconditionally.
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