Pythonic way for missing dict keys

Duncan Booth duncan.booth at invalid.invalid
Mon Jul 30 09:37:05 CEST 2007


Steven D'Aprano <steve at REMOVE.THIS.cybersource.com.au> wrote:

> 
> Instead of doing:
> 
> 
> if callable(function): function()
> 
> you should do:
> 
> try:
>     function()
> except TypeError:
>     pass
> 
> 
> That should work for most uses of callable(), but isn't quite the
> same. (What if function() has side-effects, or is expensive, and you
> want to determine if it is callable, but not actually call it _now_?)

The replacement for callable(x) is simply hasattr(x, '__call__').
Once upon a time it may have been that functions didn't have a __call__ 
attribute (I haven't checked back on really old Pythons top see if this 
was the case), but these

>> Also, what is the replacement of reduce? I think I remember seeing
>> somewhere that lists comprehension would be (but also remember the
>> advise that reduce will be quicker).
> 
> No, a list comprehension isn't equivalent to reduce(). There is no
> replacement for reduce().
<snip>
There are of course several replacements for specialised uses of reduce: 
sum, any, all. There is no general purpose replacement, but you can 
write one in a few lines if you really need it.

> 
> It's a shame really. Oh well, maybe it will sneak back in via a
> functional module, or itertools, or something. What a waste, what a
> waste.

I'm sure it will reappear in some other module, but that's the correct 
place for a little used function, not in builtins.



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