update Dockerfile to pin to Python 3.9 (#29)

fixes #28

Author: SathyaBhat

errata.md

@@ -1,13 +1,19 @@
 # Errata for *Book Title*
 
-On **page xx** [Summary of error]:
+On **page 6** [Figure captions interchanged]:
 
-Details of error here. Highlight key pieces in **bold**.
+On page 6 and page 7, the captions for **Figure 1-1 and Figure 1-2 are interchanged**. The caption for Figure 1-1 should read _Representation of three apps running on three different virtual machines_ and the caption for Figure 1-2 should read _Representation of three apps running on three different containers_.
 
 ***
 
-On **page xx** [Summary of error]:
+On **page 27** [Extra word on the sentence about inter-daemon communication]:
 
-Details of error here. Highlight key pieces in **bold**.
+On page 27, in the chapter paragraph about Docker daemon, the example sentence mentions _Some examples of inter-daemon communication include communication Datadog for container metrics monitoring and Aqua for container security monitoring_. This should **actually read** _Some examples of inter-daemon communication include Datadog for container metrics monitoring and Aqua for container security monitoring_
 
-***
+***
+
+
+For the **Telegram chat bot exercises** [Docker image has been updated]: 
+ 
+The exercises refer to Docker iamge to be used as `FROM python:3-alpine`. Due to some breaking changes in Python versions and dependencies, this causes **Docker image to not build**. 
+For this reason, the Docker images have been **updated** to refer to **Python 3.9** image and as a result, the FROM line has been updated to `FROM python:3.9-alpine` in place of the existing `FROM python:3-alpine`.

source-code/chapter-3/python-app/.gitignore

@@ -0,0 +1,59 @@
+# Byte-compiled / optimized / DLL files
+__pycache__/
+*.py[cod]
+
+# C extensions
+*.so
+
+# Distribution / packaging
+.Python
+env/
+build/
+develop-eggs/
+dist/
+downloads/
+eggs/
+.eggs/
+lib/
+lib64/
+parts/
+sdist/
+var/
+*.egg-info/
+.installed.cfg
+*.egg
+
+# PyInstaller
+#  Usually these files are written by a python script from a template
+#  before PyInstaller builds the exe, so as to inject date/other infos into it.
+*.manifest
+*.spec
+
+# Installer logs
+pip-log.txt
+pip-delete-this-directory.txt
+
+# Unit test / coverage reports
+htmlcov/
+.tox/
+.coverage
+.coverage.*
+.cache
+nosetests.xml
+coverage.xml
+*,cover
+
+# Translations
+*.mo
+*.pot
+
+# Django stuff:
+*.log
+
+# Sphinx documentation
+docs/_build/
+
+# PyBuilder
+target/
+.idea/
+last_updated.txt

source-code/chapter-4/exercise-1/docker-hello-world/Dockerfile

@@ -1,4 +1,4 @@
-FROM python:3-alpine
+FROM python:3.9-alpine
 
 LABEL description="Dockerfile for Python script which prints Hello, Name"
 

source-code/chapter-4/exercise-2/docker-multi-stage/multistage-build/Dockerfile

@@ -2,7 +2,7 @@ FROM python:3 as python-base
 COPY requirements.txt .
 RUN pip install -r requirements.txt
 
-FROM python:3-alpine
+FROM python:3.9-alpine
 COPY --from=python-base /root/.cache /root/.cache
 COPY --from=python-base requirements.txt .
 RUN pip install -r requirements.txt && rm -rf /root/.cache

source-code/chapter-4/exercise-3/newsbot/Dockerfile

@@ -1,4 +1,4 @@
-FROM python:3-alpine
+FROM python:3.9-alpine
 WORKDIR /apps/subredditfetcher/
 COPY . .
 RUN ["pip", "install", "-r", "requirements.txt"]

source-code/chapter-6/exercise-1/newsbot/Dockerfile

@@ -1,4 +1,4 @@
-FROM python:3-alpine
+FROM python:3.9-alpine
 
 RUN apk add gcc musl-dev python3-dev libffi-dev openssl-dev cargo
 WORKDIR /apps/subredditfetcher/