How can I generate n random values from a bimodal distribution in Python?

It's unclear where your problem is; it's also unclear what the purpose of the variable w is, and it's unclear how you judge you get an incorrect result, since we don't see the plot code, or any other code to confirm or reject a binomial distribution.
That is, your example is too incomplete to exactly answer your question. But I can make an educated guess.

If I do the following below:

import numpy as np
import matplotlib.pyplot as plt

N=400
mu, sigma = 100, 5
mu2, sigma2 = 10, 40
X1 = np.random.normal(mu, sigma, N)
X2 = np.random.normal(mu2, sigma2, N)
X = np.concatenate([X1, X2])
plt.hist(X)

and that yields the following figure: