Pythonic way to overwrite a default argument with **kwargs?

Question

With a function f calling another well-known function in Python (e.g. a matplotlib function), what is the most pythonic/efficient/elegant way to define some default values while still giving the possibility to the user of f to fully customize the called function (typically with **kwargs), including to overwrite the default keyword arguments defined in f?

import numpy as np
import matplotlib.pyplot as plt


v = np.linspace(-10.,10.,100)
x,y = np.meshgrid(v, v)
z = -np.hypot(x, y)

def f(ax, n=12, **kwargs):
    ax.contourf(x, y, z, n, cmap=plt.cm.autumn, **kwargs)

fig, ((ax0, ax1), (ax2, ax3)) = plt.subplots(2, 2)
f(ax0) # OK
f(ax1, n=100) # OK
f(ax2, n=100, **{'vmax': -2, 'alpha': 0.2}) # OK
# f(ax3, n=100, **{'cmap': plt.cm.cool}) # ERROR

plt.show()

Here, the last call to f throws:

TypeError: contourf() got multiple values for keyword argument 'cmap'

Answer 1

In your wrapper, you could simply adjust kwargs before passing it to wrapped function:

def f(ax, n=12, **kwargs):
    kwargs.setdefault('cmap', plt.cm.autumn)
    ax.contourf(x, y, z, n, **kwargs)

setdefault will avoid changing the argument if it was passed to your wrapper, but you could just as easily always clobber it if you wanted.