pytoolz/toolz — pull request #222 by eriknw (2014-12-16 00:17:09+00:00)
Title: Add `itemmap` and `itemfilter` to `dicttoolz`.

These complete the set of `{key,val,item}{filter,map}` functions.

Better examples and motivating use cases are welcome.

I first wanted `itemmap` to calculate a chain of mappings (so A maps to B maps to C) using a function like this:
```python
def isomorph(item):
k, v = item
return func(k), k
```

I think `itemmap(reversed, d)` to invert a dictionary is a common use case (as long as the key-values are bijective). I think `itemfilter` is less useful, but it completes the set and is potentially useful for more complicated filtering.