[Python] Iterate a function over a list of dataframes

I have 2 timeframes, for example 15 minutes and 4 hours, and want to calculate volume ma on them. I wrote a function for it, now I want to use a for loop for this purpose. But I have faced some errors.

The function:

def volume_ma(timeframe=M15, length=20):
timeframe['volume_ma'] = ta.sma(timeframe['tick_volume'], length=length)

volume_ma()


Loop:

dataframes = {'M1': M1, 'H4': H4}

for name, sublist in dataframes.items():
volume_ma(name)

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