How to use Pandas groupby in a for loop (FutureWarning)

Question

I have the following pandas dataframe:

d2 = {'col1': [0, 0, 1, 1, 2], 'col2': [10, 11, 12, 13, 14]}
df2 = pd.DataFrame(data=d2)
df2

Output:

    col1    col2
0   0       10
1   0       11
2   1       12
3   1       13
4   2       14

And I need to run the following:

for i, g in df2.groupby(['col1']):
    col1_val = g["col1"].iloc[0]
    print(col1_val)

The original code is more complex but writing so for the purpose of illustration.

And the part for i, g in df2.groupby(['col1']): gives the following warning:

FutureWarning: In a future version of pandas, a length 1 tuple will be returned 
when iterating over a groupby with a grouper equal to a list of length 1. 
Don't supply a list with a single grouper to avoid this warning.

How am I supposed to run the for loop to get rid of this warning?

Answer 1

This means that you should use a string instead of the list with a unique string:

for i, g in df2.groupby('col1'):
    col1_val = g["col1"].iloc[0]
    print(col1_val)

If you keep the original code, in the future i will have the value (0,)/(1,)/(2,) instead of 0/1/2