What is wrong with this code?

valavel

Hi I am trying to learn Python and Pythonista trying to run this downloaded code, but I get a too many values error. Any help here or in understand 3D vector fields will be appreciated.
BTW the link to this forum from the Pythonista console does not work.

# The first step is to import the required packages. The aliases `plt` and 
# `np` are coding conventions.
# * `Axes3D` allows adding 3d objects to a 2d matplotlib plot.
# * The `pyplot` submodule from the **matplotlib** library, a python 2D
# plotting library which produces publication quality figures.  
# * The `numpy` library for efficient numeric-array manipulation
from mpl_toolkits.mplot3d import Axes3D
import matplotlib.pyplot as plt
import numpy as np

# Now we set up the data to plot, the `x`, `y` and `z` arrays are the
# coordinates for the start points of each arrow, whilst the `u`, `v` and 
# `w` arrays are the coordinates of the endpoints.
x, y, z = np.meshgrid(np.arange(-0.8, 1, 0.2),
                      np.arange(-0.8, 1, 0.2),
                      np.arange(-0.8, 1, 0.8))

u = np.sin(np.pi * x) * np.cos(np.pi * y) * np.cos(np.pi * z)
v = -np.cos(np.pi * x) * np.sin(np.pi * y) * np.cos(np.pi * z)
w = (np.sqrt(2.0 / 3.0) * np.cos(np.pi * x) * np.cos(np.pi * y) *
     np.sin(np.pi * z))

# Now we create the plot with `quiver()`. The 1.4.x version of newer of the
# **matplotlib** library is required for this command to work. For the colour
# of the arrows it is possible to use either html hexadecimal codes, html
# colour names or a 3-tuple of rgb values.
fig = plt.figure()
ax = fig.gca(projection='3d')

ax.quiver(x, y, z, u, v, w,                 # data
          length=0.15,                      # arrow length
          color='Tomato'                 # arrow colour
          )

ax.set_title('3D Vector Field')             # title
ax.view_init(elev=18, azim=30)              # camera elevation and angle
ax.dist=8                                   # camera distance

plt.show()

MartinPacker

Not to try to answer your question but just to observe you're (mostly) using a large bold font in this post.

Only the code snippets are normal. I don't know if you can edit the post but anyway...

ccc

Your code works beautifully on Pythonista 3 (and produces a cool graph!) when running in both Python 2.7 mode and in Python 3.5 mode.

Your code does not work in Pythoista 2 which runs an older version of Matplotlib. I suspect that the signature of the quiver() method changed between Matplotlib 1.3 and 1.4.0 and that your code was written for 1.4 and later.

import matplotlib
print(matplotlib.__version__)  # 1.3.1 in Pythonista 2 and 1.4.0 in Pythonista 3

For posting code to this forum, please use the three backticks trick. Enter:

<a blank line>
```python <nothing else on this line>
<your code>
``` <nothing else on this line>

You can find the backtick character (`) by doing a press and hold on the ' key.

valavel35

Thank you MartinPacker in future I will try to format my posted code properly - actually it was a copy/paste situation from another source.
Thank you ccc I upgraded to Pythonista 3 and indeed the nice 3D vector plot appeared :)

valavel35

Hi After upgrading to Pythonista 3 I ended up with two apps on the ipad the old blue Py 2 and the new green Py 3. Shall I delete the Py 2 app and start all over with Py 3? BTW Some code I have been working on in Py 3 seems to have been lost.

dgelessus

Yes, Pythonista 2 and 3 are two separate apps, because Pythonista 3 is a paid upgrade. If you want to move your code from Pythonista 2 to 3, go into the Pythonista 3 settings and turn on "Pythonista 2 Files". Then a "Pythonista 2" folder will appear in the file list, and you can move the files from Pythonista 2 into Pythonista 3.

valavel35

Thanks its a very good app