[Python-ideas] Syntactic sugar to declare partial functions

[Chris Angelico]

On Tue, Aug 14, 2018 at 4:00 AM, Bruce Leban <bruce at leban.us> wrote:
> And as to saying a lambda function is an "anonymous function": the anonymity
> is not a property of the function. If I assign it to a name, it's no longer
> anonymous. Really a "lambda" or "lambda function" is just a function, but
> "lambda" is a synecdoche for "function created with a lambda expression".

True, but at that point, you get into hairy points of definitions.
Which of these functions is anonymous?

def do_stuff(callback): ...

do_stuff(do_stuff)
do_stuff(lambda: 42)
do_stuff(callback=lambda: 42)

Obviously do_stuff itself has a name. When you pass it a parameter, it
can access that as "callback", which means the function has been
assigned to a name. Does it cease to be anonymous? What if you use a
keyword argument?

Within Python, there's a fairly clear definition: if there is
something in the source code which sets the function's __name__
attribute, it's not an anonymous function. So anonymous functions come
from:

* Lambda expressions, always called "<lambda>"
* Comprehensions/genexps, always called "<listcomp>" etc
* Callable objects that aren't functions (or classes, since those have names)
* Maybe something else that I've forgotten.

You're absolutely right that a "lambda function" isn't really a thing,
in the same way that Python doesn't have "raw strings" (only "raw
string literals", which are literals which result in perfectly
ordinary strings). But the anonymity of them is a somewhat measurable
feature, even if it isn't very important. The distinction between
"lambda functions" and "def functions" is important to style guides,
but otherwise shouldn't matter.

ChrisA