>
> On what basis do you ascertain whether "==" would work correctly?
> Please explain.
Hi Chris, I'm just glancing at the line of code, and doing a little thought
experiment to see if it would get the same output if == was used instead.
For a singleton like None or False or the class like "list" .. == will
return the same answer as "is". Look at these lines;
if mode is None:
if type(items) is list:
If that code works with "is" it's going to work with == too. People are not
used to seeing == in these cases, but it works:
>>> x = None
>>> x is None
True
>>> x == None
True
>>>
>>> t = type([1, 2, 3])
>>> t is list
True
>>> t == list
True
>>>
>>> fn = list.index
>>> fn is list.index
True
>>> fn == list.index
True
The situations where "is" is truly needed are rather esoteric.
Best,
Nick
On Mon, Aug 30, 2021 at 2:02 PM Chris Angelico <ros...@gmail.com> wrote:
> On Tue, Aug 31, 2021 at 6:52 AM Nick Parlante <n...@cs.stanford.edu>
> wrote:
> >
> > I claimed that uses of "is" where it is needed for correctness
> > are quite rare. Let me back that up with a little data here.
> >
> > Just as a random supply of Python code, let's look at
> > the first four Python modules where the name starts
> > with a letter from the Python standard modules list
> > https://docs.python.org/3/py-modindex.html :
> > abc.py aifc.py argparse.py ast.py (The array module appears to be in C)
> >
> > Strip out PyDoc and string literals and just grep
> > for " is " (code included below if you'd like to try
> > it yourself). Look at those lines - how many of those
> > uses of "is" are needed for correctness, where the "is"
> > is really doing something, and how many would work
> > fine with ==? The resulting lines of code are included below.
> >
> > There's about 90 uses of is/is-not in this sample.
> > 100% of these uses would work correctly using ==.
> > Not a single one of these uses actually relies on the "is"
> > computation for correctness.
>
> On what basis do you ascertain whether "==" would work correctly?
> Please explain.
>
> ChrisA
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