Matplotlib imshow() too many objects for cmap
Question: I'm trying to create a simple imshow() plot (matplotlib v.1.2.1) of a 2D
gaussian function:

    
    
    import matplotlib.pyplot as plt
    import numpy as np
    from pylab import *
    
    def gaussian(x,y,stdx,stdy):
        return 1.0/(2*np.pi*stdx*stdy) * (np.exp(-0.5*(x**2/stdx**2 + y**2/stdy**2)))
    
    coords = np.linspace(-1,1,100)
    X,Y = np.meshgrid(coords,coords)
    std_list = np.linspace(1,2,20)
    output = [gaussian(X,Y,std_list[i],std_list[i]) for i in range(len(std_list))]
    
    for i in range(len(output)):
        plt.imshow(X,Y,np.array(output[i]),cmap='bone')
        plt.show()
    

And I get the following error:

    
    
    Traceback (most recent call last):
      File "blur.py", line 14, in <module>
        plt.imshow(X,Y,np.array(output[i]),cmap='bone')
    TypeError: imshow() got multiple values for keyword argument 'cmap'
    

In fact, to make sure I wasn't crazy, I took out the cmap argument altogether,
and now I'm getting the following error:

    
    
    Traceback (most recent call last):
      File "blur.py", line 14, in <module>
        plt.imshow(X,Y,np.array(output[i]))
      File "/home/username/anaconda/lib/python2.7/site-packages/matplotlib/pyplot.py", line     2737, in imshow
        imlim=imlim, resample=resample, url=url, **kwargs)
      File "/home/username/anaconda/lib/python2.7/site-packages/matplotlib/axes.py", line 7098, in imshow
        if norm is not None: assert(isinstance(norm, mcolors.Normalize))
    AssertionError
    

I've made sure that the arguments of imshow( ) all have the same shape, so I'm
not entirely sure what I'm doing wrong. Could this be a bug?


Answer: `imshow` doesn't take `x`, `y`, `z` as input. (`pcolor` and `pcolormesh` do,
however).

Either use `pcolormesh(x, y, z)`, or use the `extent` kwarg to imshow.

e.g.

    
    
    plt.imshow(Z, extent=[X.min(), X.max(), Y.min(), Y.max()],
               cmap='bone')
    

or

    
    
    plt.pcolormesh(X, Y, Z, cmap='bone')
    

* * *

What's happening is that `imshow` expects

    
    
    imshow(X, cmap=None, norm=None, aspect=None, interpolation=None,
             alpha=None, vmin=None, vmax=None, origin=None, extent=None,
             **kwargs)
    

Notice that the second argument is `cmap`, which explains why you're getting
the error you are when you pass in an additional `cmap` kwarg.

Hopefully that clarifies things a touch! Good luck!

