How can I understan the "for" here?

[Kermit Mei]

Hello all, look at the following sentence:

>>>params = {"server":"mpilgrim", "database":"master", "uid":"sa", "pwd":"secret"}
>>> ["%s=%s" % (k, v) for k, v in params.items()]

['pwd=secret', 'database=master', 'uid=sa', 'server=mpilgrim']

I can't understand the second sentence because of the "for ... in".
I consider that the syntactics of "for" should be:

for k,v in params.items():
......

But there's no a colon here, why it can work?

Thanks!