(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>

docker-compose.yml

@@ -1,12 +1,17 @@
 version: "3"
+
 services:
+
   bdfr:
+    build:
+      context: .
+      dockerfile: ./Dockerfile
     image: bdfr
-    build: .
+    container_name: bdfr
     ports:
       - "8080:8080"
       - "7634:7634"
     volumes:
-      - "./:/root/Bulk Downloader for Reddit"
+      - .:/bdfr:z
     container_name: bdfr_container
-    network_mode: bridge 
+    network_mode: bridge