[Python] Assign a list in a pandas dataframe cell: ValueError: Must have equal len keys and...

I was trying to

df.at[100, 'subjects']


The result is

[]


which indicates the index is unique.

But when I tried to replace the empty list to a new one:

df.at[100, 'subjects'] = [1,2,3]


the error occurred.

ValueError: Must have equal len keys and value when setting with an iterable


I met several similar cases when I tried to assign a list value to a specific cell in pandas dataframe. But I couldn't repeat this error, sometimes the valueError showed up and at other times it was just fine. I really cannot explain the reason that has caused the difference..

Thanks in advance!

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