In most circumstances for (key, val) in data won't work, as the default dictionary iterable only contains the keys. You want for key, val in data.items():
I use dictionary comprehensions personally but I have mixed feelings about the syntax. It looks too much like set comprehensions on first glance. Compare the following to see what I mean.
myset = {x for x in "This is my stuff".split()}
mydict = {x:len(x) for x in "This is my stuff".split()}
Well I see what you mean but then again a comma looks very much like a period ...
The advantage of this syntax is that : unambiguously introduces a key: value pair, whereas (key, value) could also occur in a list comprehension (e.g., by accident).
