Question

I am trying to plot some data and I am getting this error from the noted line. I googled the line but couldn’t find any meaningful discussion on this issue. I am new to Python so trying to figure this stuff out as I go along.

 pl.figure()
 ax = pl.subplot(111)
 ax.plot(Xk[:,0], Xk[:,1], '.')

 ERROR=>>> twos = (y == 2).nonzero()[0]
 for i in twos:
    imagebox = OffsetImage(X[i,:].reshape(28,28))
    location = Xk[i,0], Xk[i,1]
    ab = AnnotationBbox(imagebox, location, boxcoords='data', pad=0.)
    ax.add_artist(ab)

 pl.show()

This is the error message

 AttributeError: 'bool' object has no attribute 'nonzero'

Any clues, seems like y may not be a comparable entity.

I am trying to massage code from a sample file to get my own stuff going so forgive if this is a bit redundant.

I do appreciate the help.

Answer 1

You are trying to assign something to a varaible calles twos:

twos = (y == 2).nonzero()[0]

An Python tells you (y == 2) has no such property. And that is logic, because the
brackets cause the evaluation of the expression y == 2 which can be either True or False.

In python using . means you are trying to access a method or a property of some instance.
If you a string it has methods bounded to it, that all strings have:

In [133]: A='lorem ipsum'
# pressed Tab
In [134]: A.
A.capitalize  A.endswith    A.isalnum     A.istitle     A.lstrip      A.rjust       A.splitlines  A.translate
A.center      A.expandtabs  A.isalpha     A.isupper     A.partition   A.rpartition  A.startswith  A.upper
A.count       A.find        A.isdigit     A.join        A.replace     A.rsplit      A.strip       A.zfill
A.decode      A.format      A.islower     A.ljust       A.rfind       A.rstrip      A.swapcase    
A.encode      A.index       A.isspace     A.lower       A.rindex      A.split       A.title       

If you are new to python, numpy and matplotlib, I recommend you to start using IPython. Your learning of python will be smoother.

As an alternative to the Tab press you could do dir(someObject):

In [134]: dir(A)
Out[134]: 
['__add__',
 '__class__',
 '__contains__',
 '__delattr__',
 '__doc__',
 '__eq__',
  .... snipped...
 'startswith',
 'strip',
 'swapcase',
 'title',
 'translate',
 'upper',
 'zfill']