Can anyone please help me in resolving the error => AttributeError: Array instance has no attribute '__trunc__'
Peter Otten
__peter__ at web.de
Tue Apr 9 03:57:23 EDT 2013
bhk755 at gmail.com wrote:
> I am trying to create 2D arrays without using advanced features like
> numpy,
I'd say that using ctypes is a bit more "advanced" than *using* numpy
because with ctypes it helps to know C.
> for this I have created 2 separate modules arrays.py and
> array2D.py. Here's the code for that:
- You should absolutely go with numpy
- If you insist on building your own use lists of lists as suggested
- If you need something more space efficient than lists have a look at
http://docs.python.org/2/library/array.html
rather than ctypes.
Now on to some debugging, without looking into the details.
> import arrays
>
> class Array2D :
> # Creates a 2-D array of size numRows x numCols.
> def __init__( self, numRows, numCols ):
> # Create a 1-D array to store an array reference for each row.
>
> self._theRows = arrays.Array( numRows )
Here you create an instance of your array of integers...
> # Create the 1-D arrays for each row of the 2-D array.
> print "Num of Cloumns is", numCols
>
> for i in range( numRows ) :
> self._theRows[i] = arrays.Array( numCols )
...and here you are stuffing arrays.Array instances into that array of
integers. In nuce:
>>> import ctypes
>>> class C: pass # classic class
...
>>> items = (ctypes.c_int * 3)()
>>> items[0] = C()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: C instance has no attribute '__trunc__'
ctypes unhelpfully tries to truncate the value to convert it into an
integer. As an aside here's an example of a successful conversion:
>>> class C2:
... def __trunc__(self): return 42
...
>>> items[0] = C2()
>>> items[0]
42
There are basically two resolutions:
- adjust the type of the outer array or
- use a single 1D array internally and calculate the index as
row * width + column (for example).
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