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From: Ian Kelly <ian.g.kelly@gmail.com>
Date: Mon, 19 Mar 2012 17:20:43 -0600
Subject: Re: Currying in Python
To: Kiuhnm <kiuhnm03.4t.yahoo.it@mail.python.org>
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Xref: csiph.com comp.lang.python:21909

I hope you don't mind if I critique your code a bit!

On Fri, Mar 16, 2012 at 7:21 PM, Kiuhnm
<kiuhnm03.4t.yahoo.it@mail.python.org> wrote:
> Here we go.
>
> --->
> def genCur(f, unique =3D True, minArgs =3D -1):

It is customary in Python for unsupplied arguments with no default to
use the value None, not -1.  That's what it exists for.

> =A0 =A0""" Generates a 'curried' version of a function. """
> =A0 =A0def geng(curArgs, curKwargs):
> =A0 =A0 =A0 =A0def g(*args, **kwargs):
> =A0 =A0 =A0 =A0 =A0 =A0nonlocal f, curArgs, curKwargs, minArgs; =A0 =A0# =
our STATIC data
>
> =A0 =A0 =A0 =A0 =A0 =A0if len(args) or len(kwargs):

Collections evaluate as true if they are not empty, so this could just be:

            if args or kwargs:

> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0# Allocates data for the next 'g'. We don'=
t want to modify our
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0# static data.
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0newArgs =3D curArgs[:];
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0newKwargs =3D dict.copy(curKwargs);
>
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0# Adds positional arguments.
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0newArgs +=3D args;
>
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0# Adds/updates keyword arguments.
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0if unique:
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0# We don't want repeated keyword a=
rguments.
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0for k in kwargs.keys():
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0if k in newKwargs:
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0raise(Exception("R=
epeated kw arg while unique =3D True"));
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0newKwargs.update(kwargs);

Since you're writing this for Python 3 (as evidenced by the use of the
nonlocal keyword), you could take advantage here of the fact that
Python 3 dictionary views behave like sets.  Also, you should use a
more specific exception type:

                if unique and not kwargs.keys().isdisjoint(newKwargs):
                    raise ValueError("A repeated keyword argument was suppl=
ied")

> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0# Checks whether it's time to evaluate f.
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0if minArgs >=3D 0 and minArgs <=3D len(new=
Args) + len(newKwargs):

With minArgs defaulting to None, that would be:

                if minArgs is not None and minArgs <=3D len(newArgs) +
len(newKwargs):

> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0return f(*newArgs, **newKwargs); =
=A0 =A0# f has enough args
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0else:
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0return geng(newArgs, newKwargs); =
=A0 =A0# f needs some more args
> =A0 =A0 =A0 =A0 =A0 =A0else:
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0return f(*curArgs, **curKwargs); =A0 =A0# =
the caller forced the evaluation
> =A0 =A0 =A0 =A0return g;
> =A0 =A0return geng([], {});
>
> def cur(f, minArgs =3D -1):
> =A0 =A0return genCur(f, True, minArgs);
>
> def curr(f, minArgs =3D -1):
> =A0 =A0return genCur(f, False, minArgs);

The names "cur" and "curr" are terrible.  Good names should describe
what the function does without being too onerous to type, and the
addition of the duplicate "r" is not an obvious mnemonic for
remembering that the first one prohibits duplicate keyword arguments
and the second one allows them.  Why not more descriptive names like
"curry" and "curry_unique"?

That's all I've got.  All in all, it's pretty decent for a Python newbie.

Cheers,
Ian