[Python-Dev] What's the status of PEP 505: None-aware operators? (original) (raw)

Random832 random832 at fastmail.com
Wed Nov 29 12:03:09 EST 2017

On Tue, Nov 28, 2017, at 15:31, Raymond Hettinger wrote:

> I also cc python-dev to see if anybody here is strongly in favor or against this inclusion. Put me down for a strong -1. The proposal would occasionally save a few keystokes but comes at the expense of giving Python a more Perlish look and a more arcane feel. One of the things I like about Python is that I can walk non-programmers through the code and explain what it does. The examples in PEP 505 look like a step in the wrong direction. They don't "look like Python" and make me feel like I have to decrypt the code to figure-out what it does. timeout ?? localtimeout ?? globaltimeout 'foo' in (None ?? ['foo', 'bar']) requestedquantity ?? defaultquantity * price name?.strip()[4:].upper() user?.firstname.upper()

Since we're looking at different syntax for the ?? operator, I have a suggestion for the ?. operator - and related ?[] and ?() that appeared in some of the proposals. How about this approach?

Something like (or None: ...) as a syntax block in which any operation [lexically within the expression, not within e.g. called functions, so it's different from simply catching AttributeError etc, even if that could be limited to only catching when the operand is None] on None that is not valid for None will yield None instead.

This isn't entirely equivalent, but offers finer control.

v = name?.strip()[4:].upper() under the old proposal would be more or less equivalent to:

v = name.strip()[4:].upper() if name is not None else None

Whereas, you could get the same result with: (or None: name.strip()[4:].upper())

Though that would technically be equivalent to these steps: v = name.strip if name is not None else None v = v() if v """"" v = v[4:] """"""" v = v.upper """"""" v = v() """""""

The compiler could optimize this case since it knows none of the operations are valid on None. This has the advantage of being explicit about what scope the modified rules apply to, rather than simply implicitly being "to the end of the chain of dot/bracket/call operators"

It could also be extended to apply, without any additional syntax, to binary operators (result is None if either operand is None) (or None: a

[I think I proposed this before with the syntax ?(...), the (or None: ...) is just an idea to make it look more like Python.]

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