raise_on_error : boolean, default True
     Whether to raise on invalid data types (e.g. trying to where on strings)

>>> import pandas as pd
>>> df = pd.DataFrame(data=[1,2,3])
>>> df.where(df == 'a', raise_on_error=False)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File ".../pandas/core/ops.py", line 1290, in f
    res = self._combine_const(other, func, raise_on_error=False)
  File ".../pandas/core/frame.py", line 3634, in _combine_const
    raise_on_error=raise_on_error)
  File ".../pandas/core/internals.py", line 3162, in eval
    return self.apply('eval', **kwargs)
  File ".../pandas/core/internals.py", line 3056, in apply
    applied = getattr(b, f)(**kwargs)
  File ".../pandas/core/internals.py", line 1181, in eval
    repr(other))
TypeError: Could not compare ['a'] with block values

1288             # straight boolean comparisions we want to allow all columns
1289             # (regardless of dtype to pass thru) See #4537 for discussion.
1290             res = self._combine_const(other, func, raise_on_error=False)
1291             return res.fillna(True).astype(bool)

1157         # get the result
1158         try:
1159             with np.errstate(all='ignore'):
1160                 result = get_result(other)
1161 
1162         # if we have an invalid shape/broadcast error
1163         # GH4576, so raise instead of allowing to pass through
1164         except ValueError as detail:
1165             raise
1166         except Exception as detail:
1167             result = handle_error()
1168 
1169         # technically a broadcast error in numpy can 'work' by returning a
1170         # boolean False
1171         if not isinstance(result, np.ndarray):
1172             if not isinstance(result, np.ndarray):
1173 
1174                 # differentiate between an invalid ndarray-ndarray comparison
1175                 # and an invalid type comparison
1176                 if isinstance(values, np.ndarray) and is_list_like(other):
1177                     raise ValueError('Invalid broadcasting comparison [%s] '
1178                                      'with block values' % repr(other))
1179 
1180                 raise TypeError('Could not compare [%s] with block values' %
1181                                 repr(other))