How do I extract the list inside a string in Python?

Question

I imported a CSV using Pandas and one column was read in with string entries. Examining the entries for this Series (column), I see that they should actually be lists. For example:

df['A'] = pd.Series(['["entry11"]', '["entry21","entry22"]', '["entry31","entry32"]'])

I would like to extract the list elements from the strings. So far, I've tried the following chain:

df['A'] = df['A'].replace("'",'',regex=True).
                  replace('\[','',regex=True).
                  replace('\]','',regex=True).
                  str.split(",")

(all on one line, of course).

and this gives me back my desired list elements in one column.

• ['"entry11"']
• ['"entry21", "entry22"']
• ['"entry31", "entry32"']

My question: Is there a more efficient way of doing this? This seems like a lot of strain for something that should be a little easier.

Answer 1

You can "apply" the ast.literal_eval() to the series:

In [8]: from ast import literal_eval

In [9]: df['A'] = df['A'].apply(literal_eval)

In [10]: df
Out[10]: 
                    A
0           [entry11]
1  [entry21, entry22]
2  [entry31, entry32]

There is also map() and applymap() - here is a topic where the differences are discussed:

• Difference between map, applymap and apply methods in Pandas