Koichi Hori

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Using Python on Windows

(Diary of an Old AI Researcher who is still Programming)

9 March 2019

I usually use only mac.
However, I began to feel that even a MacBook Air is heavy since I was about 62 years old.
So, I have bought a light Windows laptop FMV U75B (748g) in 2018 .

At first, I used this Windows laptop only for presentation, mail, and office document processing. (For presentation, I presented html files on Windows, which were written by my own program on mac. I do not use PowerPoint, because I do not like PowerPoint.)
Well, but, I got too impatient to modify and test my programs during my business trip, many times. :-)
Should I throw away the Windows laptop and return to the MacBook Air?
My colleague said returning to MacBook Air was the best choice, but I determined to install Python on my Windows laptop, because I did not want to throw away the laptop I just bought.


Following is a note of a few tips to use Python on Windows.

Installing Python on Windows

First of all, installing Python3 on Windows is easy.
We can download the installation package from
https://www.python.org/downloads/windows/ .

I could install the Python3.7 without any problems on my Windows laptop.


Running Python on Windows

Note that the command to run Python3 is not 'python3' but 'python' or 'py' regardless of the installed version, on Windows.


Reading and writing unicode files by Python on Windows

Reading or writing files including unicode multi-byte characters causes 'UnicodeDecodeError', which does not happen on mac.
To fix this problem, we should add 'encoding="utf-8"' when we open the files. For example,

open(filename, "r", encoding="utf-8")



Using subprocess.run on Windows

I used, in my program, subprocess.run to copy a file to another, i.e.


import subprocess
subprocess.run(["cp", '/Users/hori/mysystem/templatefile.html', myworkingfile])

I must change "cp" to "copy", since this is Window OS, of course.
Moreover, I must change the slash into backslash. That's crazy, isn't it? But this is Windows, of course.
The code,

subprocess.run(["copy", '\Users\hori\mysystem\templatefile.html', myworkingfile])

does not work, either.
We must escape the backslash by putting another backslash like '\\Users\\hori...'.
Instead, to make the code simpler, we can use the raw string of Python (r + string), and the code is

subprocess.run(["copy",r'\Users\hori\mysystem\templatefile.html', myworkingfile])


OK, finally, my Python program began to run on Windows laptop, too.


(We need not replace slash by backslash in the file name when using "open". E.g., the code:

open('/Users/hori/mysystem/templatefile.html', "r", encoding="utf-8")

works, because Python deals with the OS dependent file path syntax.)




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