[Python] AttributeError: 'numpy.ndarray' object has no attribute 'append'

I am trying to run the code presented on the second page:

http://ocw.mit.edu/courses/electric...fall-2008/video-lectures/lecture-20/lec20.pdf

At the bottom of the code you have to add these lines:

simFlips(100,100)

show()


Here is the error that I get when I run it on ubuntu:

Traceback (most recent call last):
File "coin.py", line 36, in <module>
simFlips(100,100)
File "coin.py", line 16, in simFlips
diffs.append(abs(heads - tails))
AttributeError: 'numpy.ndarray' object has no attribute 'append'


What am I doing wrong that gives me the last error?

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