Question

here goes my first ever question, im doing a basic logplayer from data in a txt file:

the code is something like:

    for aircraft in self.logArray.itervalues():

        for logLine in aircraft:
            currentPoint = self.point(logLine[1], logLine[2])
            currentPoint = self.win2canvas(currentPoint)
            points = np.append(points, currentPoint)

        print points
        print np.size(points)
        self.canvas.create_line(points)
        points = np.array([])

So logArray is a dictionary, each name contains an array of kind [time,x,y], so there will be an array like that for each aircraft name.

The second for simply converts to tkinter canvas coords and appends the currentPoint to the pre-existing (and initialized).

When it gets to the create_line method, i get:

File "/home/joao/tese/workspace/ATC/src/autoATC/LogPlayer.py", line 131, in drawPath
self.canvas.create_line(points)
  File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 2204, in create_line
return self._create('line', args, kw)
  File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 2192, in _create
*(args + self._options(cnf, kw))))
_tkinter.TclError: wrong # coordinates: expected an even number, got 399

I’ve manually checked the size of the points array and is indeed even numbered. So i double-checked using np.size, which returned 398!

I’ve also tried using a very similar test approach, doing:

    self.canvas.create_line([123,345,234,453,23,34,45,56,67,78]) 

which went perfectly! I don’t get why, but somehow my points array ends up getting an extra element, and I don’t know where from!

Thank you for your time and patience!

Answer 1

I believe that the issue is that you are using numpy arrays for this. The call stack here looks like this

1. Tkinter.py, line 2160, in
   create_line return
   self._create(‘line’, args, kw)
2. Tkinter.py, line 2148, in _create
   *(args + self._options(cnf, kw))))
3. numeric.py, line 1424, in array_str
   return array2string(a,
   max_line_width, precision,
   suppress_small, ‘ ‘, “”, str)
4. arrayprint.py, line 307, in
   array2string return lst

If you have np.array([0., 0., 200., 100.]) the string that is returned by array2string() is ‘[ 0. 0. 100. 200.]’. I suspect that then it gets split returning the list of [‘[‘, ‘0.’, ‘0.’, ‘100.’, ‘200.]’] which has one extra element ‘[‘.

You code should work if you use a list in place of np.array() or even if you just cast the numpy array to a list, like:

self.canvas.create_line(list(points))

Although, I would think that using a list from the start is more straight forward if you don’t need to use the functionality of numpy arrays.