[Python] replace values of a column (but keep NA values) with list of other values python

I would like to start since I am looking for tips on how to tackle this issue, rather than specific code with an answer I have not provided any code, just my situation. Is this allowed? Or am I still required to provide some form of code? I am unsure on these guidelines so if this is not allowed please inform me and I will not do this next time

I have the following dataframe:

well​

sample
A1​

1
NaN​

2
NaN​

3
A2​

1
NaN​

2
A3​

1
NaN​

2
NaN​

3​

Is it possible to replace the values in the column 'well' (thus the A1, A2, A3 etc) with the values of a list? I have made a list = [0,31,20] for example and need the well names replaced by this list or I need an extra column with the values of the list on the same row as the well name (thus other rows in the column need to stay NaN)

I have tried working with for example df.replace() where I tried using a dictionary in stead of list, or using the list but these approaches did not work. I hope to obtain tips on how to tackle this issue (thus not specific codes with the answer, I am still learning python therefore tips could help me in the learning process rather than specific pieces of code with a solution)

To visualise below the two options I am searching for as final dataframe:

Option 1

well​

sample
0​

1
NaN​

2
NaN​

3
31​

1
NaN​

2
20​

1
NaN​

2
NaN​

3​

Or option 2:

well​

sample​

Position
A1​

1​

0
NaN​

2​

NaN
NaN​

3​

NaN
A2​

1​

31
NaN​

2​

NaN
A3​

1​

20
NaN​

2​

NaN
NaN​

3​

NaN​

Thank you in advance for your help!

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