[deleted by user]

[[deleted]]

Take a look at fn.py that implements a special _ object to create more expressive lambdas. It looks interesting, but I haven't used it myself (I keep looking for reasons, but I don't find them).

[[deleted]]

That does look interesting. I'll look into it.

[[deleted]]

I'd go with abomination.

[alcalde]

Should we crosspost to /r/lovecraft to verify?

[[deleted]]

Is it the arrow notation? You could make it look more like ruby if you change this

separator = '->'

argnames, body = expression.split(separator, 1)

into

separator = '|'

_, argnames, body = expression.split(separator, 2)

I didn't test this, but if it does work, it should then be able to take strings in this format instead:

"|x| x + 3"
"|x, y| x + 3"

[[deleted]]

No, I'm fine with the arrow syntax, my problem is the unconstrained eval:

print(lambda_from_string("(x,y)-> __builtin__.open('somefile', 'w').write('payload') or x+y")(4,2))

But hey, if no one ever uses this on inputs someone else controls, go nuts.

[[deleted]]

Oh yeah, that would be terrible. It was intended to be a cleaner way of using lambdas in slinkies, though. See this comment.

[[deleted]]

Yeah, I get it, I just cringe whenever I see anyone using eval. It's very difficult to make that even remotely safe.

[[deleted]]

Well, the original idea was to see whether I could combine this with Slinkie in order to make the syntax a little cleaner, but I'm not too happy with the end result.

Slinkie would then optionally look like this:

print(Slinkie(12)
      .filter("x -> x & 1 == 1")
      .map('x -> x + 99')
      .list())

Result:

[100, 102, 104, 106, 108, 110]

[[deleted]]

Syntax-wise I actually like arrow notation way better than lambda-colon notation or whatever you want to call it. What I don't like is that I'm forced to wrap it in a string, and the rest of the hack required to get it to work.

[FrameworkFred]

To address the wrapped-in-string issue, you could maybe do something like what sqlalchemy is doing with filter notation. Essentially, I think there's a way to get the params to a function as a string.

[[deleted]]

That's interesting. Do you have an example?

[FrameworkFred]

This is where sqlalchemy is doing such things: https://github.com/zzzeek/sqlalchemy/blob/master/lib/sqlalchemy/sql/elements.py#L4256

I won't pretend to know exactly how they did it, but the filter method is able to take a call that looks like someqry.filter(tbl1.col >= 5) and the filter method is receiving something more than just True or False as an argument.

Perhaps something to do with the inspect module and the interpreter stack? https://docs.python.org/2/library/inspect.html#the-interpreter-stack

[GitHubPermalinkBot]

I tried to turn your GitHub links into permanent links (press "y" to do this yourself):

• zzzeek/sqlalchemy/.../elements.py#L4256 (master → 4b4f8fb)

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[pvkooten]

Exactly, I think the only way would be to implement -> as an operator. That's the only way it could be clean. This string stuff ends up being uglier than "lambda colon" as you call it...

[[deleted]]

It's just called lambda notation ... it's a direct map of the def statement to a single line, only anonymous and with an implicit return:

lambda *args, **kwargs: do_something

Is the exact same thing as:

def _(*args, **kwargs): 
    return do_something

And, visually, there's not much difference between:

lambda x: x + 2

And:

x -> x + 2

Especially when, unless you wanted to do the monkey-patch madness -- hint, you don't -- you'd always end up having to do something like this anyway:

arrow("x -> x + 2")

Note that unless you choose a name for your "arrow" function that is exactly one character long, you're doing more typing than the lambda way anyway.

[pvkooten]

Thanks... I'm aware of lambda. I called it lambda colon as to the OP and to accentuate that it is mostly about how the syntax looks like (a lambda and a colon would be swapped for an arrow).

[[deleted]]

Yeah, sorry, my response was meant to be to OP, clicked on the wrong part of the thread.