On Mon, Oct 25, 2021 at 08:39:19AM -0000, Jeremiah Vivian wrote:
> If I wanted to check if an *exact* object is in an iterable
A nice way to check for exact identity in an iterable is this:
any(value is element for element in iterable)
That stops on the first match, and is pretty efficient. To reverse the
check, "not in", use the obvious `not any(...)` as above.
"element is in iterable" reads nicely, but the difference between that
and "element in iterable" is subtle and problematic.
Especially for English speakers, where "x in y" is strictly speaking
grammatically incorrect:
Wrong: if George in Europe, send him an email
Right: if George is in Europe, send him an email
I'm surely not the only one who occassionally puts in an unwanted
`is` into `in` tests. Fortunately that is a syntax error now.
Otherwise, it would silently do the wrong thing. And then the coder who
accidentally inserts an unneeded `is` into the test will have to deal
with weird implementation-dependent silent failures due to caching of
small ints and strings:
5 is in range(10) # may succeed in CPython, but fail in Jython
5000 is in range(4000, 6000) # will probably fail everywhere
5000 is in [4000, 5000, 6000] # may succeed in CPython
x = 5000
x is in [4000, 5000, 6000] # may or may not succeed
int('5000') is in [4000, 5000, 6000] # probably fail
"a" is in "cat" # probably succeed in CPython
"cat" is in "caterpiller" # definitely fail
"CAT".lower() is in ['bat', 'cat', 'dog'] # possibly fail
So although the syntax reads nicely, it would be a bug magnet.
--
Steve
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