memory leak in matplotlib histogram

Question

Running the following code will result in memory usage rapidly creeping up.

import numpy as np
import pylab as p
mu, sigma = 100, 15
x = mu + sigma*np.random.randn(100000)
for i in range(100):
    n, bins, patches = p.hist(x, 5000)

However, when substituting the call to pylab with a direct call to the numpy histogram method then memory usage is constant (it also runs significantly faster).

import numpy as np
mu, sigma = 100, 15
x = mu + sigma*np.random.randn(100000)
for i in range(100):
    n, bins = np.histogram(x, 5000)

I was under the impression that pylab is using the numpy histogram function. There must be a bug somewhere...

Answer 1

Matplotlib generates a diagram. NumPy does not. Add p.show() to your first code to see where the work goes.

import numpy as np
import pylab as p
mu, sigma = 100, 15
x = mu + sigma*np.random.randn(100000)
n, bins, patches = p.hist(x, 5000)
p.show()

You may want to try with a smaller number for np.random.randn(100000) first to see something quickly.

EDIT

Does not really make sense to create the same plot 100 times.