In [1]: import numpy as np In [2]: a = np.arange(4) In [3]: np.pad(a,2) --------------------------------------------------------------------------- ValueError Traceback (most recent call last) <ipython-input-3-f56fe53684b8> in <module>() ----> 1 np.pad(a,2) /usr/lib64/python3.3/site-packages/numpy/lib/arraypad.py in pad(array, pad_width, mode, **kwargs) 1331 elif mode is None: 1332 raise ValueError('Keyword "mode" must be a function or one of %s.' % -> 1333 (list(allowedkwargs.keys()),)) 1334 else: 1335 # Drop back to old, slower np.apply_along_axis mode for user-supplied ValueError: Keyword "mode" must be a function or one of ['edge', 'constant', 'wrap', 'reflect', 'median', 'maximum', 'minimum', 'symmetric', 'linear_ramp', 'mean']. In [4]: np.__version__ Out[4]: '1.9.0b1' The documentation specify that the mode parameter is optional I am getting the same for both python 2.7 and 3.3 OS: Gentoo linux Nadav