turn"string-like"listintointwithpython

After after retrieving some data, some rows of my dataframe are composed by "string-like" lists, like this one:

       bar                foo
   0     'A'                1
   1     'B'                2
   2     'B'     "['2' ,'3']"
   3     'B'              '4'
   4     'C'     "['5' ,'3']"

How could I turn the foo column into int values and take the bigger value with python pandas?