python 3.x - Pandas add space between characters if needed -

given following data frame:

import pandas pd import numpy np df = pd.dataframe({'a':['one[p]','two [n]'], })  df     0   one[p] 1   2 [n] 

i'd add space before open bracket ('[') if 1 not exist (for tall column).

the desired result is:

    0   1 [p] 1   2 [n] 

thanks in advance!

or can use:

df.loc[~df.a.str.contains(r' \['), 'a'] = df.a.str.replace('[',' [') print df          0  1 [p] 1  2 [n]