It seems that ma.array does not accept a sequence which contains a masked scalar array (not sure if this is the correct term). Is this deliberate? #numpy 1.0b5, python 2.3.x, winXP import numpy as N print N.ma.array([1,2,3, N.ma.array(1, mask=True)]) Traceback (most recent call last): File "C:\eclipse\plugins\org.python.pydev.debug_1.2.2\pysrc\pydevd_comm.py", line 529, in doIt result = pydevd_vars.evaluateExpression( self.thread_id, self.frame_id, self.expression, self.doExec ) File "C:\eclipse\plugins\org.python.pydev.debug_1.2.2\pysrc\pydevd_vars.py", line 258, in evaluateExpression exec expression in frame.f_globals, frame.f_locals File "<string>", line 1, in ? File "C:\Python23\Lib\site-packages\numpy\core\ma.py", line 562, in __init__ c = numeric.array(data, dtype=tc, copy=True, order=order) TypeError: an integer is required #works fine if scalar masked array is not masked print N.ma.array([1,2,3, N.ma.array(1)]) [1 2 3 1]