[Python-ideas] Keyword declarations

Carl Smith carl.input at gmail.com
Wed May 16 15:03:18 EDT 2018

If `def(if=3)...` works implicitly, then why not make `if = 3`, `x.if
= 3`, `import
if`, `def if` and `class if` implicit too?

Another issue is what happens here:

keyword if
import if
f.if = 3

The keyword will be a valid name in old code, so you need to be able to
reference it as a name in code that uses it as a keyword.

-- Carl Smith
carl.input at gmail.com

On 16 May 2018 at 18:24, Adam Bartoš <drekin at gmail.com> wrote:

> Hello,
> I have yet another idea regarding the the clashes between new keywords and
> already used names. How about introducing two new keywords *wink* that
> would serve as lexical keyword/nonkeyword declarations, similarly to
> nonlocal and global declarations?
> def f():
>     nonkeyword if
>     if = 2 # we use 'if' as an identifier
>     def g():
>         keyword if
>         if x > 0: pass # now 'if' again introduces a conditional statement
> This allows to have a name as both identifier and keyword in a single
> module, and since it's lexical, it could be in principle syntax-highlighted
> correctly.
> When a new keyword is added to the list of standard keywords like 'given'
> or 'where', a module that uses the name as identifier could be easily fixed
> by a global declaration 'nonkeyword given'. Maybe even exception messages
> pointing to this could be added. If 'nonkeyword keyword' is allowed, we can
> also fix code using the name 'keyword' as an identifier, but doing so in
> the global scope couldn't be undone.
> On the other hand, new language features depending on new keywords could
> be made provisionary by not adding the keywords to the standard list, so
> people who would like to use them would need to opt in by e.g. 'keyword
> given'. Surely, this provisional mechanism isn't robust at all since new
> features may just extend the usage of current keywords.
> Declaring a keyword that has no meaning in the language would result in an
> exception:
> keyword foo # SyntaxError: undefined keyword 'foo'
> It should be possible to use a keyword as a parameter name without need to
> declare it in the surrounding scope, the local declaration would suffice:
> # nonkeyword if # not needed
> def f(if=3): # ok
>     nonkeyword if
> Other option is to interpret parameters always as nonkeywords or to raise
> a special syntax error when a keyword occurs at a place of a formal
> parameter (similarly to 'def f(x): nonlocal x').
> Clearly, even if this proposal diminished the cost of adding new keywords,
> the cost would still be high.
> Best regards,
> Adam Bartoš
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