Erroneous example in official Python tutorial (Chapter 9.10)?

Question

I copied the following example from Python 3.6.1 Documentation, Chapter 9.10 into Jupyter Notebook (Python version 3.6.1):

xvec = [10, 20, 30]

yvec = [7, 5, 3]

sum(x*y for x,y in zip(xvec, yvec))         # dot product

While the official documentation says that it would print 260 , I got the following error in Notebook:

----> 4 sum(x*y for x,y in zip(xvec, yvec))
TypeError: 'int' object is not callable

This is definitely not just a question on 'int object is not callable', but more on the palpable error in what is considered to be the gospel for Python.

Answer 1

If by mistake you have overwritten zip() or/and sum() , which leads that your current code will not work. You can restore their default functionalities using del , like this example:

>>> zip = [1]
>>> zip
[1]
>>> del zip
>>> zip
<function zip>

So, you can try :

>>> del zip
>>> del sum
>>> xvec = [10, 20, 30]
>>> yvec = [7, 5, 3]
>>> sum(x*y for x,y in zip(xvec, yvec))

And it will output:

260

Answer 2

The code should work as long as you didn't overwrite zip or sum :

>>> xvec = [10, 20, 30]
>>> yvec = [7, 5, 3]
>>> sum(x*y for x,y in zip(xvec, yvec))
260

Make sure that you didn't overwrite them:

>>> sum = 0  # <--- overwrite
>>> sum(x*y for x,y in zip(xvec, yvec))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'int' object is not callable