Create this script in IDLE and save it as
exitstatus.py.
import sys
print("About to return exit status 123.")
sys.exit(123)
On macOS,
cd /Users/myname/python python3 exitstatus.py About to return exit status 123. echo $? 123
On PC,
cd C:\Users\Myname\python py.exe exitstatus.py About to return exit status 123. echo %errorlevel% 123
These Python programs do not call the
print
function
and therefore they produce no output.
But they do produce an exit status number.
ibm.py
gets the current price of IBM stock from
this web page.
temperature.py
gets the current temperature in New York from
this file
in JSON format.""" strand.py Exit with exit status 0 if the Strand bookstore is currently open, 1 if closed. """ import sys import datetime d = datetime.datetime.now() #number of hours after midnight currentHour = d.hour + (d.minute + (d.second + d.microsecond / 1_000_000) / 60) / 60 if currentHour >= 12 + 10.5: #10:30 p.m. sys.exit(1) #Strand has closed for the night. if d.weekday() == 6: #Sunday openingHour = 11 #11:00 a.m. else: openingHour = 9.5 # 9:30 a.m. if openingHour <= currentHour: sys.exit(0) #Strand is already open. else: sys.exit(1) #Stand hasn't opened up yet this morning.
See
man 5 localtime
$ date Mon Feb 10 11:21:45 UTC 2020 $ cd /etc $ pwd /etc $ ls -l localtime lrwxrwxrwx 1 root root 25 Feb 7 12:28 localtime -> ../usr/share/zoneinfo/UTC $ sudo ln -sf ../usr/share/zoneinfo/US/Eastern localtime $ ls -l localtime lrwxrwxrwx 1 root root 32 Feb 10 06:23 localtime -> ../usr/share/zoneinfo/US/Eastern $ date Mon Feb 10 06:23:32 EST 2020 $ cd /usr/share/zoneinfo/US $ pwd /usr/share/zoneinfo/US $ ls -l Eastern -rw-r--r-- 3 root root 3545 Oct 23 16:47 Eastern $ file Eastern Eastern: timezone data, version 2, 5 gmt time flags, 5 std time flags, no leap seconds, 236 transition times, 5 abbreviation chars $ od -c Eastern | head -4 0000000 T Z i f 2 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 0000020 \0 \0 \0 \0 \0 \0 \0 005 \0 \0 \0 005 \0 \0 \0 \0 0000040 \0 \0 \0 354 \0 \0 \0 005 \0 \0 \0 024 200 \0 \0 \0 0000060 236 246 036 p 237 272 353 ` 240 206 \0 p 241 232 315 `
SSL stands for Secure Sockets Layer. CA stands for Certification Authority. TLS stands for Transport Layer Security. If the above Python script gives you the following message on macOS,
urllib.error.URLError: <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:749)>run the command
certifi
package and create a text file named
cacert.pem.
CA stands for Certification Authority.
pip3 list certifi (2019.9.11) pip3 show certifi Name: certifi Version: 2019.9.11 Summary: Python package for providing Mozilla's CA Bundle. Home-page: https://certifi.io/ Author: Kenneth Reitz Author-email: me@kennethreitz.com License: MPL-2.0 Location: /Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages Requires: Required-by: requests cd /Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages ls -ld certifi* drwxr-xr-x 7 myname mygroup 224 Oct 15 22:49 certifi drwxr-xr-x 9 myname mygroup 288 Oct 15 22:49 certifi-2019.9.11.dist-info
When you open a Terminal window on macOS, or bash shell window on Linux,
the commands in the file
~/.bash_profile
are automatically executed.
I put the following commands into the
~/.bash_profile
on my Mac.
if python3 /Users/myname/python/ibm.py then #ibm.py produced exit status 0. echo The price of IBM is at least 140. else #ibm.py did not produce exit status 0. echo The price of IBM is less than 140. mail nervous@investor.com < formletter.txt fi
Your Python script should produce an exit status number
because the thing that runs the script might not be a human being.
It might be another program
(e.g.,
~/.bash_profile),
and that other program might expect to receive an exit status
from your script.