Binary operations over array of workspaces do not work similar to them working on a single workspace from Python

[abuts]

This issue was originally TRAC 9957

lets assume workspaces w1, w1s, w2 and w2s are loaded in Mantid and can be added together

then the script:

w1=mtd['w1']
ws=mtd['w1s']
w2=mtd['w2']
w2s=mtd['w2s']


ws+=w1;
w2s+=w2;

works as expected and ws and w2s after the script are the sum of the
initial workspace and the addendum.

If, from other side, one tries to work like this:

w1=[mtd['w1'],mtd['w2']]
ws=[mtd['ws'],mtd['w2s']]

for i in xrange(len(ws)):
   ws[i]+=w1[i]
   print "Sum workspace has {0} events in it".format(ws[i].getNumberEvents())

result will be different and ws and w2s in Mantid will remain unchanged despite print row in the loop would report that the workspaces are added together (print will work if the workspaces are event workspaces).

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