title: Pandas : finding out wrong data
body: <p>Let's says there is a pandas data frame as below:
  {a:[1,2,3,4],
   b:[1,2,3,?]}
  Assuming values within the strings 'a' and 'b' are more than a thousand, and we do not know yet there is '?' in the series b. Thus, we are keeping having 'object type' when it comes to 'b'</p>
  
  <p>How can we find out at which row exist non-float(non-integer) value?</p>