(maint) code clean up (#187)

## bdfr

- Add the bound instance as method parameter
- Change methods not using its bound instance to staticmethods
- Fix dangerous default argument
- Refactor the comparison involving `not`
- Refactor unnecessary `else` / `elif` when `if` block has a `raise` statement
- Refactor unnecessary `else` / `elif` when `if` block has a `return` statement
- Refactor useless `else` block in the loop
- Remove implicit `object` from the base class
- Remove reimported module
- Remove unnecessary generator
- Remove unnecessary return statement
- Remove unnecessary use of comprehension
- Remove unused imports
- Use `is` to compare type of objects
- Using not x can cause unwanted results

## Dockerfile

- use a pinned Python version tag instead of latest
- leverage cached requirements

Signed-off-by: Vladislav Doster <mvdoster@gmail.com>

Co-authored-by: Ali Parlakçı <parlakciali@gmail.com>

Dockerfile

@@ -1,9 +1,31 @@
-FROM python:latest
+# Bulk Downloader for Reddit
+#
+# VERSION               0.0.1
+
+FROM python:3.8-slim-buster
+LABEL Description="This image enables running Buld Downloader for Reddit with in a container environment" Version="0.0.1"
+
+ENV PYTHONUNBUFFERED 1
+ENV PYTHONDONTWRITEBYTECODE 1
 
-WORKDIR "/root/Bulk Downloader for Reddit"
-COPY ./requirements.txt ./
-RUN ["pip", "install", "-r", "requirements.txt"]
 EXPOSE 8080
 EXPOSE 7634
 
-CMD ["python", "script.py", "-d", "downloads"]
+# Install dependencies for building Python packages
+RUN apt-get update \
+  && apt-get install -y build-essential \
+  && apt-get purge -y --auto-remove -o APT::AutoRemove::RecommendsImportant=false \
+  && rm -rf /var/lib/apt/lists/*
+  
+# Requirements are installed here to ensure they will be cached.
+COPY requirements.txt /requirements.txt 
+RUN pip install --no-cache-dir -r /requirements.txt \
+    && rm -rf /requirements.txt
+
+# Copy project files into container
+COPY . /bdfr
+WORKDIR /bdfr
+
+# This is useful because the image name can double as a reference to the binary 
+ENTRYPOINT ["python", "script.py"]
+CMD ["--help"]