问题
I have some code right now that is getting stuck on one line:
perm = numpy.random.permutation(128)
To which it give the following error: "TypeError: len() of unsized object." I can't figure out what the issue is since 128 is just an integer. I see that this is a problem that has probably been resolved before here: http://mail.scipy.org/pipermail/numpy-discussion/2007-January/025592.html but their solution isn't helpful to me since it is about floats.
Can anyone see what's going wrong here?
回答1:
In Sage, the input is preparsed by the Sage preparser.
I'll use 12 instead of 128 so the examples fit in one line.
When you input the following:
sage: import numpy
sage: perm = numpy.random.permutation(12)
The error message you get looks like:
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-3-38b6a5e3e889> in <module>()
----> 1 perm = numpy.random.permutation(Integer(12))
/opt/sage/local/lib/python2.7/site-packages/numpy/random/mtrand.so in mtrand.RandomState.permutation (numpy/random/mtrand/mtrand.c:21297)()
/opt/sage/local/lib/python2.7/site-packages/numpy/random/mtrand.so in mtrand.RandomState.shuffle (numpy/random/mtrand/mtrand.c:20965)()
TypeError: len() of unsized object
where you see in particular the line:
----> 1 perm = numpy.random.permutation(Integer(12))
telling you that your input
perm = numpy.random.permutation(12)
was preparsed to
perm = numpy.random.permutation(Integer(12))
However numpy is not so happy being fed a Sage Integer, it would prefer a Python int.
The simplest way to input a raw Python integer is to append r to it:
sage: perm = numpy.random.permutation(12r)
This will work for you:
sage: perm = numpy.random.permutation(12r)
sage: perm # random
array([ 9, 0, 11, 4, 2, 10, 3, 5, 7, 6, 1, 8])
Another way is to let Sage transform the Python int to a Sage Integer but then force it to convert it back to a Python integer:
sage: perm = numpy.random.permutation(int(12))
sage: perm # random
array([ 5, 9, 1, 7, 0, 2, 10, 6, 3, 8, 4, 11])
Another thing you could do is to turn off the Sage preparser.
sage: preparser(False)
sage: perm = numpy.random.permutation(12)
sage: perm # random
array([ 0, 2, 7, 5, 8, 11, 1, 6, 9, 10, 3, 4])
来源：https://stackoverflow.com/questions/28426920/unsized-object-error-with-numpy-random-permutation