In [4]: ll = [['one','two',1,1.23],['four','five',4,34.3],['six','seven',4,34.3]]

In [5]: np.array(ll)
Out[5]:
array([['one', 'two', '1', '1.23'],
       ['four', 'five', '4', '34.3'],
       ['six', 'seven', '4', '34.3']],
       dtype='|S5')

In [8]: np.array([tuple(x) for x in ll],dtype='S5,S5,i,f')
Out[8]:
array([('one', 'two', 1, 1.2300000190734863),
       ('four', 'five', 4, 34.29999923706055),
       ('six', 'seven', 4, 34.29999923706055)],
      dtype=[('f0', 'S5'), ('f1', 'S5'), ('f2', '<i4'), ('f3', '<f4')])