"ValueError: Length of values (2) does not match length of index (1)" when using pandas.insert

Question

I am not sure why I am receiving the error message when all I am trying to do is to insert a list into a specific cell of pandas dataframe.

Here is the extractor function

def extractor():
    .
    .
    .
    df4 = df3.drop(dropped_columns, axis=1, errors='ignore')
    df5 = df4.drop([1], axis=0, errors='ignore')
    # I know that df3.iloc[0, 0] is always a string of characters or ''
    df5.insert(0, "Sequence", stringSplitter4(df3.iloc[0, 0]))
    .
    .
    .

This is the Utilities function used in extractor

def stringSplitter4(a_string: str) -> List:
    """This function splits a string in every other appearance of opening parantheses"""
    return list(accumulate(findall('(?<![^)]).+?(?![^(])', a_string)))

And, here is the complete error message I am receiving:

Traceback (most recent call last):
  File "c:/Users/username/Desktop/Project/my_script.py", line 91, in <module>
    main()
  File "c:/Users/username/Desktop/Project/my_script.py", line 71, in main
    extractor(path, pep_id)
  File "c:\Users\username\Desktop\Project\Utilities.py", line 253, in extractor
    df5.insert(
  File "C:\ProgramData\Anaconda3\lib\site-packages\pandas\core\frame.py", line 4418, in insert
    value = self._sanitize_column(value)
  File "C:\ProgramData\Anaconda3\lib\site-packages\pandas\core\frame.py", line 4509, in _sanitize_column
    com.require_length_match(value, self.index)
  File "C:\ProgramData\Anaconda3\lib\site-packages\pandas\core\common.py", line 531, in require_length_match
    raise ValueError(
ValueError: Length of values (2) does not match length of index (1)

Answer 1

As Jorge mentioned in his comment, I had to convert my list into a string first and then insert it into the cell. I would later, into the code, take care of the string by exploding it into a list in the right place of the code.

Instead of:

def stringSplitter4(a_string: str) -> List:
    """This function splits a string in every other appearance of opening parantheses"""
    return list(accumulate(findall('(?<![^)]).+?(?![^(])', a_string)))

I did:

def stringSplitter4(a_string: str) -> List:
    """This function splits a string in every other appearance of opening parantheses"""
    sequence_lst = list(accumulate(findall('(?<![^)]).+?(?![^(])', a_string)))
    return '[' + ', '.join(sequence_lst) + ']'