Hi all.
There's some really unintuitive/inconsistent behaviour with theano's scan
and I'm wondering how I should work around it.
Take the following test, which I would expect to pass:
import theano
import theano.tensor as tt
def test_scan_tuple_output():
x = tt.matrix()
def mul_by_2_and_3(data):
return (data*2, data*3)
y, updates = theano.scan(mul_by_2_and_3, sequences=[x])
assert len(y)==2
assert len(updates)==0
def mul_by_2(data):
return (data*2, )
y, updates = theano.scan(mul_by_2, sequences = [x])
assert len(y)==1
assert len(updates) == 0
if __name__ == '__main__':
test_scan_tuple_output()
It fails on
It
It fails on
assert len(y)==1
with "TypeError: object of type 'TensorVariable' has no len()" because if
scan detects a tuple of length-1, it just returns the data inside this
tuple.
This becomes annoying when trying to make a scannable function with
variable return length, (one of which can be one).
Is there a way I can make scan not totally change its behaviour when the
tuple of returned arguments happens to have length 1?
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