Improve datetime.py script and README.md documentation with comments and tips from linting

Author: kso512

README.md

@@ -8,23 +8,23 @@ Install Raspbian Buster and Wire the printer according to [this](https://learn.a
 
 Run a test to see if the printer is working by punching in these commands into the terminal.
 
-```
+``` shell
 stty -F /dev/serial0 19200
 echo -e "This is a test.\\n\\n\\n" > /dev/serial0
 ```
 
 ### Installing
 
-Update the system and install prequisities.
+Update the system and install prerequisites.
 
-```
+``` shell
 sudo apt-get update
 sudo apt-get install git cups wiringpi build-essential libcups2-dev libcupsimage2-dev python3-serial python-pil python-unidecode
 ```
 
 Install the printer driver. Don't worry about the warnings that g++ gives.
 
-```
+``` shell
 git clone https://github.com/adafruit/zj-58
 cd zj-58
 make
@@ -33,14 +33,14 @@ sudo ./install
 
 Make the printer the default printer. This is useful if you are going to be doing other things with it.
 
-```
+``` shell
 sudo lpadmin -p ZJ-58 -E -v serial:/dev/serial0?baud=19200 -m zjiang/ZJ-58.ppd
 sudo lpoptions -d ZJ-58
 ```
 
 Restart the system. Clone this repository and try to run *printertest.py*.
 
-```
+``` shell
 git clone https://github.com/galacticfan/Python-Thermal-Printer/
 cd Python-Thermal-Printer
 python3 printertest.py

__pycache__/Adafruit_Thermal.cpython-37.pyc

@@ -1,19 +1,37 @@
-#!/usr/bin/python3
-# pylint: disable=E1101,W0614
+#!/usr/bin/env python3
+
+# Python3 script to print the current date and time, using
+#   the Adafruit_Thermal library, in ISO 8601 format.
+# https://www.iso.org/iso-8601-date-and-time-format.html
 
 import time
 from Adafruit_Thermal import *
 
+# Lines of margin (integer)
 i_feed = 3
+# Seconds to pause (float)
 f_pause = 1.0
 
-printer = Adafruit_Thermal("/dev/serial0", 19200, timeout=5)
+# Define the printer port, speed, and timeout
+printer = Adafruit_Thermal("/dev/ttyS0", 19200, timeout=5)
 
+# Build the date stamp in the format YYYY-MM-DD ex: "2021-12-25"
 datestamp = time.strftime("%Y-%m-%d", time.gmtime())
 print ("Date in preferred format:", datestamp)
+
+# Build the time stamp in the format Thh:mm:ssZ ex: "T23:59:59Z"
 timestamp = 'T' + time.strftime("%H:%M:%S", time.gmtime()) + 'Z'
 print ("Time in preferred format:", timestamp)
 
+# Tell printer to sleep
+printer.sleep()
+# Sleep for the defined time in case we're called many times in a row
+time.sleep(f_pause)
+# Call wake() before printing again, even if reset
+printer.wake()
+# Restore printer to defaults
+printer.setDefault()
+
 # Give a little room at the top
 printer.feed(i_feed)
 # Center justify
@@ -26,13 +44,3 @@
 printer.println(timestamp)
 # Give a little room at the bottom
 printer.feed(i_feed)
-
-# Tell printer to sleep
-printer.sleep()
-# Call wake() before printing again, even if reset
-printer.wake()
-# Restore printer to defaults
-printer.setDefault()
-
-# Sleep for one second in case we're called many times
-time.sleep(f_pause)