dictionary comprehension in Python

Question

Is there a way to the follwing in dictionary comprehension?

bmcdsreg = {}
for key, val in bms.iteritems():
    bmcdsreg[key] = {}
    for reg in bmmaps.columns:
        bmcdsreg[key][reg]= val*bmmaps[reg]

I have the following version where the keys are interchanged:

bmcdsreg = {reg: {key: val*bmmaps[reg] for key, val in bms.iteritems()}
             for reg in bmmaps.columns}

Answer 1

Here is how:

bmcdsreg = {
    key: {reg: val * bmmaps[reg] for reg in bmmaps.columns}
    for key, val in bms.items()
}