Python pandas insert list into a cell

Since set_value has been deprecated since version 0.21.0, you should now use at. It can insert a list into a cell without raising a ValueError as loc does. I think this is because at always refers to a single value, while loc can refer to values as well as rows and columns.

df = pd.DataFrame(data={'A': [1, 2, 3], 'B': ['x', 'y', 'z']})

df.at[1, 'B'] = ['m', 'n']

df =
    A   B
0   1   x
1   2   [m, n]
2   3   z

You also need to make sure the column you are inserting into has dtype=object. For example

>>> df = pd.DataFrame(data={'A': [1, 2, 3], 'B': [1,2,3]})
>>> df.dtypes
A    int64
B    int64
dtype: object

>>> df.at[1, 'B'] = [1, 2, 3]
ValueError: setting an array element with a sequence

>>> df['B'] = df['B'].astype('object')
>>> df.at[1, 'B'] = [1, 2, 3]
>>> df
   A          B
0  1          1
1  2  [1, 2, 3]
2  3          3