approximation

[scidam]

You have two issues with your code:
1) def applog(a,x): should be def applog(n,x):

2)You need to add the following lines to your code:

y = [applog(4, _) for _ in x]
plt.plot(x, y,color='blue', label='approx ln(x)' ) 

In my code, I used np.vectorize decorator to be able to pass vectors to the applog function.
E.g. after applying np.vectorize we are able to pass vectors to applog: e.g. applog(4, [1,2,3,4,5]) is allowed now.
So, if don't want to use np.vectorize you need to precompute y-values corresponding
to x-values. This is why I add a line y = .....