Why are arbitrary target expressions allowed in for-loops?

Question

I accidentally wrote some code like this:

foo = [42]
k = {\'c\': \'d\'}

for k[\'z\'] in foo:  # Huh??
    print k

But to my surprise, this

Answer 1

Every name is just a dictionary key*.

for x in blah:

is precisely

for vars()['x'] in blah:

* (though that dictionary needn't be implemented as an actual dict object, in case of some optimizations, such as in function scopes).