Update values in pandas columns based on values from another DataFrame

Two DataFrames df1 and df2 both has Weight in lb columns
if Weight in lb matches I need to update the corresponding BMI in df1 from df2.

DataFrame
df1=

DataFrame
df2=

I tried

df1['BMI'] = df2.loc[df2['Weight in lb'].isin(df1['Weight in lb'],'BMI']

But it is not working, I cannot do merge operation because the original dataframe is too complex for that

Desired Output
df1=

>Solution :

You can use df2 to make a mapping from weight to BMI and then use it on df1

weight_to_bmi = dict(df2.values)
df1['BMI'] = df1['Weight in lb'].map(weight_to_bmi)