[NumPy-Tickets] [NumPy] #1433: numpy array captures 'in' statement when it shouldn't

NumPy Trac numpy-tickets@scipy....
Tue Mar 16 17:27:46 CDT 2010

#1433: numpy array captures 'in' statement when it shouldn't
 Reporter:  graik         |       Owner:  somebody
     Type:  defect        |      Status:  new     
 Priority:  normal        |   Milestone:          
Component:  numpy.core    |     Version:  1.3.0   
 Keywords:  __contains__  |  
 The following code used to work perfectly well with older numpy versions:

 >>> a = arange(10)
 >>> a in (0,None)

 Now it gives an error:
 ValueError: The truth value of an array with more than one element is
 ambiguous. Use a.any() or a.all()

 This comes unexpected. For example my library contains several situations
 like this:

 def calculate( a=None ):
   if a in (0,None):
       a = zeros( 10 )
 calculate( a=arange(10) )

 So I use the 'in' to quickly check for identity with a couple of non-valid

 Apparently, the numpy array code now captures the 'in' statement via
 __contains__ and expects an array on the other side (not even a list will
 do). This is not logical. While there *might* be some reason for treating
 the 'array in array' situation differently, this should not break standard
 python behavior.

 Simple python lists do accept this code::

 >>> l = [1,2,3]
 >>> l in (None,0)

 I would expect numpy arrays to do the same (as it did before). At the very
 least, the new __contains__ should check for non-array arguments and fall
 back to the standard behavior rather than raising an exception.

 Thanks in advance!

Ticket URL: <http://projects.scipy.org/numpy/ticket/1433>
NumPy <http://projects.scipy.org/numpy>
My example project

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