[Python] How to filter through a defaultdict?

I have a CSV input file that I organized as a defaultdict:

{
'1234' : [('1,60', 'text', 'supplier1')],
'3456' : [('1,98', 'another text', 'supplier2')],
['1,54', 'text again', 'supplier1'],
'709' : [('2,90', 'again', 'supplier2')]
}


I would like to is prioritize tuples containing "supplier1". If there are results for the same key for supplier1 and 2, keep only supplier1. And if no results for a given key for supplier1, keeping results with other suppliers.

EDIT : desired output :

{
'1234' : [('1,60', 'text', 'supplier1')],
'3456' : ['1,54', 'text again', 'supplier1'],
'709' : [('2,90', 'again', 'supplier2')]
}

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