[Python] Pandas merge one-to-many [duplicate]

I'm trying to merge two pandas DataFrames on multiple columns. It is a many-to-one relationship. There are many of the same values in df1 but only value in df2.

These are the example DataFrames :

df1 = pd.DataFrame({'date':['2025-03-01','2025-03-01', '2025-03-02'],'period':[1,1,2], 'company':['aa','aa','b']})

df2 = pd.DataFrame({'date':['2025-03-01', '2025-03-02'],'period':[1,2],'company':['aa','b'], 'value':[4,8]})


The result I want is this (where the value '4' is only joined once on the first match and subsequent rows are filled with empty space or null):

date period company value
0 2025-03-01 1 aa 4
1 2025-03-01 1 aa null
2 2025-03-02 2 b 8


I'm trying a left join - but I get the incorrect output:

date period company value
0 2025-03-01 1 aa 4
1 2025-03-01 1 aa 4
2 2025-03-02 2 b 8

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