can't require a function named `f`

[porterjamesj]

It took me a while to figure this one out:

def f(x):
    return(x)

@require(f):
def g(y):
    return f(y)

gives:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-86-98a37b0c736a> in <module>()
----> 1 @require(f)
      2 def g(y):
      3     return f(y)
      4

/usr/local/lib/python2.7/dist-packages/IPython/parallel/controller/dependency.pyc in require(*objects, **mapping)
    133     for name, obj in mapping.items():
    134         mapping[name] = can(obj)
--> 135     return depend(_require, *names, **mapping)
    136
    137 class Dependency(set):

TypeError: __init__() got multiple values for keyword argument 'f'

I believe the cause is the use of f as a name in the constructor here.

This seems like a bit of an arbitrary restriction; it may not be possible to get around having to forbid the use of some function name, but at least we could maybe use something less likely to collide with users' things (_f maybe?).

[minrk]

yeah, poor choice of argument names. I'll make it something less likely to collide.