Updates

Author: garyns

BookCover.png

@@ -2,6 +2,24 @@
 
 The code in this repository accompanies the Packt Book Practical Python Programming for IoT, published by Packt.
 
+![Practical Python Programming for IoT Book Cover](./BookCover.png)
+
+[Table of Contents (PDF)](./TableOfContents1stEd.pdf)
+
+--- 
+
+## Purchasing Practical Python Programming for IoT
+
+Practical Python Programming for IoT is available through Packt and Amazon.
+
+* [Amazon US](https://www.amazon.com/Practical-Python-Programming-IoT-WebSockets/dp/1838982469/ref=sr_1_1)
+* [Amazon AU](https://www.amazon.com.au/Practical-Python-Programming-IoT-WebSockets-ebook/dp/B08K3MD5Z1)
+* [Packt](https://www.packtpub.com/product/practical-python-programming-for-iot/9781838982461)
+
+--- 
+
+## Repository Contents
+
 ## [Errata](errata) - Corrections and clarifications to the published content
 
 ## [Chapter 1](chapter01) - Setting Up Your Development Environment

README.md

@@ -2,6 +2,8 @@
 
 ## Chapter 2 - Introduction to Python and IoT
 
+Please see [Errata](../errata/README.md) for corrections and clarifications to the content and code found in the published book.
+
 * `requirements.txt` - Python dependencies required for this chapter
 
 * `led_gpiozero.py` - Flashing a LED using GPIOZero

TableOfContents1stEd.pdf

@@ -19,33 +19,33 @@
 
 # LED provides 'Output'
 pi.set_mode(LED_GPIO_PIN, pigpio.OUTPUT)
-pi.write(LED_GPIO_PIN, 0) # LED Off
+pi.write(LED_GPIO_PIN, 0)  # LED Off
 
 
 # Button provides 'Input'
-pi.set_mode(BUTTON_GPIO_PIN, pigpio.INPUT)                                    # (1)
-pi.set_pull_up_down(BUTTON_GPIO_PIN, pigpio.PUD_UP)                           # (2)
-pi.set_glitch_filter(BUTTON_GPIO_PIN, 10000) # microseconds debounce          # (3)
+pi.set_mode(BUTTON_GPIO_PIN, pigpio.INPUT)                                       # (1)
+pi.set_pull_up_down(BUTTON_GPIO_PIN, pigpio.PUD_UP)                              # (2)
+pi.set_glitch_filter(BUTTON_GPIO_PIN, 100000)  # 100000 microseconds = 0.1 secs  # (3)
 
 
 # Button pressed handler
-def pressed(gpio_pin, level, tick):                                           # (4)
+def pressed(gpio_pin, level, tick):                                              # (4)
     # Get current pin state for LED.
-    led_state = pi.read(LED_GPIO_PIN)                                         # (5)
+    led_state = pi.read(LED_GPIO_PIN)                                            # (5)
 
-    if led_state == 1:                                                        # (6)
+    if led_state == 1:                                                           # (6)
         # LED is on, so turn it off.
-        pi.write(LED_GPIO_PIN, 0) # 0 = Pin Low = Led Off
+        pi.write(LED_GPIO_PIN, 0)  # 0 = Pin Low = Led Off
         print("Button pressed: Led is off")
-    else: # 0
+    else:  # 0
         # LED is off, so turn it on.
-        pi.write(LED_GPIO_PIN, 1) # 1 = Pin High = Led On
+        pi.write(LED_GPIO_PIN, 1)  # 1 = Pin High = Led On
         print("Button pressed: Led is on")
 
 
 # Register button handler.
-pi.callback(BUTTON_GPIO_PIN, pigpio.FALLING_EDGE, pressed)                    # (7)
+pi.callback(BUTTON_GPIO_PIN, pigpio.FALLING_EDGE, pressed)                       # (7)
 
 print("Press button to turn LED on and off.")
 
-signal.pause() # Stops program from exiting.
+signal.pause()  # Stops program from exiting.

chapter02/README.md

@@ -32,7 +32,7 @@
 # Initialize Logging
 logging.basicConfig(level=logging.WARNING)  # Global logging configuration
 logger = logging.getLogger('main')  # Logger for this module
-logger.setLevel(logging.INFO) # Debugging for this file.                           # (2)
+logger.setLevel(logging.INFO)  # Debugging for this file.                           # (2)
 
 
 # Initialize GPIO
@@ -72,7 +72,7 @@ def get_latest_dweet():
     r = requests.get(resource)                                                     # (7)
 
     if r.status_code == 200:                                                       # (8)
-        dweet = r.json() # return a Python dict.
+        dweet = r.json()  # return a Python dict.
         logger.debug('Last dweet for thing was %s', dweet)
 
         dweet_content = None
@@ -95,7 +95,7 @@ def poll_dweets_forever(delay_secs=2):
         if dweet is not None:
             process_dweet(dweet)                                                   # (12)
 
-        sleep(delay_secs)                                                          # (13)
+            sleep(delay_secs)                                                      # (13)
 
 
 def stream_dweets_forever():
@@ -106,7 +106,7 @@ def stream_dweets_forever():
     session = requests.Session()
     request = requests.Request("GET", resource).prepare()
 
-    while True: # while True to reconnect on any disconnections.
+    while True:  # while True to reconnect on any disconnections.
         try:
             response = session.send(request, stream=True, timeout=1000)
 
@@ -115,7 +115,7 @@ def stream_dweets_forever():
                     try:
                         json_str = line.splitlines()[1]
                         json_str = json_str.decode('utf-8')
-                        dweet = json.loads(eval(json_str)) # json_str is a string in a string.
+                        dweet = json.loads(eval(json_str))  # json_str is a string in a string.
                         logger.debug('Received a streamed dweet %s', dweet)
 
                         dweet_content = dweet['content']
@@ -125,7 +125,7 @@ def stream_dweets_forever():
                         logger.error('Failed to process and parse dweet json string %s', json_str)
 
         except requests.exceptions.RequestException as e:
-            #Lost connection. The While loop will reconnect.
+            # Lost connection. The While loop will reconnect.
             #logger.error(e, exc_info=True)
             pass
 
@@ -143,13 +143,13 @@ def process_dweet(dweet):
     led_state = dweet['state']
 
     if led_state == last_led_state:                                                # (14)
-        return; # LED is already in requested state.
+        return  # LED is already in requested state.
 
     if led_state == 'on':                                                          # (15)
         led.on()
     elif led_state == 'blink':
         led.blink()
-    else: # Off, including any unhandled state.
+    else:  # Off, including any unhandled state.
         led_state = 'off'
         led.off()
 
@@ -189,6 +189,6 @@ def signal_handler(sig, frame):
         process_dweet(last_dweet)
 
     print('Waiting for dweets. Press Control+C to exit.')
-    #Only use one of the following. See notes later in Chapter.
-    #stream_dweets_forever() # Stream dweets real-time.
-    poll_dweets_forever() # Get dweets by polling a URL on a schedule.             # (19)
+    # Only use one of the following. See notes later in Chapter.
+    # stream_dweets_forever() # Stream dweets real-time.
+    poll_dweets_forever()  # Get dweets by polling a URL on a schedule.            # (19)

chapter02/button_pigpio.py

@@ -2,45 +2,63 @@
 
 This page contains corrections and clarifications to the content found in the published book.
 
-## Chapter 2
+## Chapter 2 - Understanding the breadboard
 
-### Page 43 - Breadboard Examples
+Page 44 printed 1st edition; Page 42 PDF 1st edition.
 
-**Incorrect Text**
+![Code Example](./Chapter2a.jpg)
 
-The 3rd bullet point reads _"A2 is not electrically connected to B2 (they don't share the same row)."_. This statement is incorrect because A2 _is_ electrically connected to B2 because they do share the same row.
+---
 
-**Corrected Text**
+## Chapter 2 - Responding to a button press with PiGPIO
 
-The 3rd bullet point should be _"A2 is not electrically connected to **A3** (they don't share the same row)."_.
+Page 67 printed 1st edition; Page 65 PDF 1st edition.
 
+![Code Example](./Chapter2c.png)
 
-### Page 72 - poll_dweets_forever() function
+Under the sub heading **Button pin configuration**, we see a snippet of code from the file [chapter02/button_pigpio.py](../chapter02/button_pigpio.py)
 
-There is a 4 space indentation missing in the code example for the function `poll_dweets_forever()` at line 13. The effect of this means the statement `sleep(delay_secs)` is outside the `while` block and the loop never incurs the delay. 
+At line 3 `set_glitch_filter` has the parameter 10000, which is the debounce time measured in __microseconds__.
 
-This error does not affect a readers ability to successfully run the example, but it does make the following paragraph describing line 13 practically incorrect as the code does not incur the 2-second delay mentioned.
+The proceeding paragraph states the value is in __milliseconds__, which is incorrect.
 
-The following image illustrates the issue.
+In this example, the timeout is therefore 10000 / 1000000 = 0.01 seconds
 
-![Code Example](./Chapter2Page72.png)
+This difference in timing value is not expected to affect the reader's ability to complete the exercise. However, should the example behave erratically when the button is pressed, the reader should change the parameter at line 3 from `10000` to `100000` to make the debounce time 0.1 seconds. The corrected line will therefore be:
 
-### Page 64 - Responding to a button press with PiGPIO
+```
+pi.set_glitch_filter(BUTTON_GPIO_PIN, 100000)         # (3)
+```
 
-Under the heading **Button pin configuration**, we see a snippet of code from the file `chapter02/button_gpiozero.py`
+This code change has been applied to the file [chapter02/button_pigpio.py](../chapter02/button_pigpio.py) in this repository.
 
-At line 3 `set_glitch_filter` has the parameter 10000, which is the debounce time measured in __microseconds__.
+---
 
-The proceeding paragraph states the value is in __milliseconds__, which is incorrect.
+## Chapter 2 - poll_dweets_forever() method
 
-![Code Example](./Chapter2Page65.png)
+Page 74 printed 1st edition; Page 72 PDF 1st edition.
 
-In this example, the timeout is therefore 10000 / 1000000 = 0.01 seconds
+![Code Example](./Chapter2b.png)
 
-This difference in timing value is not expected to affect the reader's ability to complete the exercise. However, should the example behave erratically when the button is pressed, the reader should change the parameter at line 3 from `10000` to `100000` to make the debounce time 0.1 seconds. The corrected line will therefore be:
+
+Under the heading **poll_dweets_forever() method**, we see a snippet of code from the file [chapter02/dweet_led.py](../chapter02/dweet_led.py)
+
+There is a 4 space indentation missing in the code example for the function `poll_dweets_forever()` at line 13. The effect of this means the statement `sleep(delay_secs)` is outside the `while` block and the loop never incurs the delay. 
+
+This error does not affect a readers ability to successfully run the example, but it does make the paragraph (as pictured above) practically incorrect as the code does not incur the 2-second delay at line 13.
+
+The corrected block of code is:
 
 ```
-pi.set_glitch_filter(BUTTON_GPIO_PIN, 100000)         # (3)
+def poll_dweets_forever(delay_secs=2):
+    """Poll dweet.io for dweets about our thing."""
+    while True:
+        dweet = get_latest_dweet()                 # (11)
+        if dweet is not None:
+            process_dweet(dweet)                   # (12)
+
+            sleep(delay_secs)                      # (13)
 ```
 
-Also note that earlier in the chapter on Page 63, we see a code example from file `chapter02/button_gpiozero.py` using a debounce time of 0.1 seconds. The error on Page 64 and in file `chapter02/button_gpiozero.py` mean that the GPIOZero and PiGPIO examples are not strictly identical, although from an illustrative perspective for the purposes of the chapter they can be considered functionally identical.
+
+This code correction has been applied to the file [chapter02/dweet_led.py](../chapter02/dweet_led.py) in this repository.