On 18/03/24 04:11, Peter J. Holzer via Python-list wrote:
On 2024-03-17 17:15:32 +1300, dn via Python-list wrote:
On 17/03/24 12:06, Peter J. Holzer via Python-list wrote:
On 2024-03-16 08:15:19 +0000, Barry via Python-list wrote:
On 15 Mar 2024, at 19:51, Thomas Passin via Python-list
<python-list@python.org> wrote:
I've always like writing using the "or" form and have never gotten bit
I, on the other hand, had to fix a production problem that using “or”
introducted.
I avoid this idiom because it fails on falsy values.
Perl has a // operator (pronounced "err"), which works like || (or),
except that it tests whether the left side is defined (not None in
Python terms) instead of truthy. This still isn't bulletproof but I've
found it very handy.
So, if starting from:
def method( self, name=None, ):
rather than:
self.name = name if name else default_value
ie
self.name = name if name is True else default_value
These two lines don't have the same meaning (for the reason you outlined
below). The second line is also not very useful.
the more precise:
self.name = name if name is not None or default_value
or:
self.name = default_value if name is None or name
Those are syntax errors. I think you meant to write "else" instead of
"or".
Yes, exactly. That's the semantic of Perl's // operator.
JavaScript has a ?? operator with similar semantics (slightly
complicated by the fact that JavaScript has two "nullish" values).
Thanks Peter!
(yes, sad consequences of suffering a neighbor's party-til-midnight
followed by an 0530 meeting-start - children: don't code exhausted!)
Herewith, an illustration of how the corrected version of the above
works - and how (in what seem unusual cases) it avoids any truthy/falsy
confusion, as raised earlier in this thread:
>>> default_value = "default"
>>> name = "Fred Flintstone"
>>> name if name is not None else default_value
'Fred Flintstone'
>>> name = None
>>> name if name is not None else default_value
'default'
>>> name = False
>>> name if name is not None else default_value
False
>>> name = 1
>>> name if name is not None else default_value
1
>>> name = 0
>>> name if name is not None else default_value
0
Personally: I find the above coding more logical, because our primary
interest is on 'the happy case', ie where the value has been assigned
(to "name"); and the default_value is only applied as a "guard".
On the other hand, I dislike the not-condition because it forces me to
think (and maybe dust-off DeMorgan). Accordingly:
>>> name = "Fred Flintstone"
>>> default_value if name is None else name
'Fred Flintstone'
>>> name = None
>>> default_value if name is None else name
'default'
>>> name = False
>>> default_value if name is None else name
False
...
YMMV!
NB your corporate Style Guide may prefer 'the happy path'...
--
Regards,
=dn
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