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From: Peter Otten <__peter__@web.de>
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Subject: Re: what is new with int conversion in Python 3
Date: Sun, 22 May 2016 10:32:48 +0200
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Xref: csiph.com comp.lang.python:108937

Sayth Renshaw wrote:

Read carefully:

>  Run from the command line as follows
> 
>   python vectorsum.py n
> 
>  where n is an integer that specifies the size of the vectors.

So to run the script with Python 3 you could do

$ python3 vectorsum.py 42

in the shell. This implicitly sets sys.argv[1] to "42" so that the 
conversion

size = int(sys.argv[1]) 

can succeed. This conversion failed because as the traceback indicates

> ValueError                                Traceback (most recent call 
last)
> <ipython-input-8-a54a878f293d> in <module>()
>      37    return c
>      38 
> ---> 39 size = int(sys.argv[1])
>      40 
>      41 start = datetime.now()
> 
> ValueError: invalid literal for int() with base 10: '-f'
> 

sys.argv[1] is "-f" which is not a valid (base-10) integer. This value 
probably got into ipython3 because you invoked it with something like

$ ipython3 console -f foo
Python 3.4.3 (default, Oct 14 2015, 20:28:29) 
Type "copyright", "credits" or "license" for more information.

IPython 1.2.1 -- An enhanced Interactive Python.
?         -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help      -> Python's own help system.
object?   -> Details about 'object', use 'object??' for extra details.

In [1]: import vectorsum
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-1-b0b6e1aba9f9> in <module>()
----> 1 import vectorsum

/home/petto/vectorsum.py in <module>()
     37    return c
     38 
---> 39 size = int(sys.argv[1])
     40 
     41 start = datetime.now()

ValueError: invalid literal for int() with base 10: '-f'

In [2]: ! python3 vectorsum.py 42
The last 2 elements of the sum [65600, 70602]
PythonSum elapsed time in microseconds 106
The last 2 elements of the sum [65600 70602]
NumPySum elapsed time in microseconds 121

By the way, I had to fix another problem to make the "In [2]:" invocation 
work. Let's see if you can do that yourself.