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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.

share|improve this question

2 Answers 2

up vote 0 down vote accepted

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']
share|improve this answer
    
Just to clarify, while here y == 2 is returning a bool, it doesn't have to return True or False. If y were a numpy array (which presumably it was in the original code) then it'd return an array of bools, and that would have a nonzero method. – DSM Oct 25 '12 at 3:56
    
@DSM, good point. In that case one could use a try and except or before hand check that y is a numpy array. Thanks for pointing that out. – Oz123 Oct 25 '12 at 9:49
up vote 0 down vote

The following works for me (from iPython):

In [11]: y = arange(5); (y==2).nonzero()[0]
Out[11]: array([2])

while the following does not:

In [13]: y = range(5);  (y==2).nonzero()[0]
------------------------------------------------------------
Traceback (most recent call last):
  File "<ipython console>", line 1, in <module>
AttributeError: 'bool' object has no attribute 'nonzero'

So as the comment by @DSM suggests - make sure that y is a numpy array and not just some list or any other object

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