Pythonanywhere: matplotlib.pyplot.imgopen creates a numpy.array that cannot be modified

I am having a problem editing the pixels of an image using matplotlib.

Python 3.7.5 (default, Nov 14 2019, 22:26:37) 
>>> import matplotlib.pyplot as plt
>>> img = plt.imread('allo.JPG')
>>> img[0][0]
array([255, 255, 255], dtype=uint8)
>>> img[0][0][1]
255
>>> img[0][0][1]=40
Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
ValueError: assignment destination is read-only

I've explored the error in various ways to no avail. Ideas?

Solution

The writeable flag is set to False for that img array.

You can make a copy and it will have the flag set to True:

>>> img.flags
  C_CONTIGUOUS : True
  F_CONTIGUOUS : False
  OWNDATA : False
  WRITEABLE : False
  ALIGNED : True
  WRITEBACKIFCOPY : False
  UPDATEIFCOPY : False

>>> img1 = img.copy()
>>> img1.flags
  C_CONTIGUOUS : True
  F_CONTIGUOUS : False
  OWNDATA : True
  WRITEABLE : True
  ALIGNED : True
  WRITEBACKIFCOPY : False
  UPDATEIFCOPY : False