Fixed most of flake8 issues

.travis.yml

@@ -1,6 +1,6 @@
 language: python
 
-# Python 3.6.7 as of 2020-10-19
+# TravisCI uses Python 3.6.7 as of 2020-10-19
 # python:
   # - "2.7"
   # - "3.5"

docs/developer-notes.md

@@ -6,9 +6,9 @@
 
 ## Code
 
-    * migrate to newer version of Python
     * test GUI
     - optional
+      - fix flake8 warning (newer version of flake8 and/or pycodestyle=2.4+)
       - remove log files in the end of the test (or create them in folder)
       - implement one more topic as an excersize
       - overall code cleaning
@@ -22,11 +22,13 @@
 
 # NOTES
 
-    - on macOS used default Python2.7
-    - without pip installed nose using '$ sudo easy_install nose', all tests have passed
+    - Python virtual environment
+      $ python3 -m venv tutorial-env
+      $ source tutorial-env/bin/activate
+      $ deactivate # if needed
 
 
-    - dependencies installation
+    - Dependencies installation
        69  easy_install pip
        70  sudo easy_install pip
        95  pip install -r requirements.txt
@@ -37,7 +39,5 @@
    89  pip install configparser==3.5
    99  PATH="/Users/kirill-personal/Library/Python/2.7/bin:$PATH"
 
-    - Python virtual environment
-      $ python3 -m venv tutorial-env
-      $ source tutorial-env/bin/activate
-      $ deactivate # if needed
+    - list available versions of the package
+      $ pip3 install flake8==

requirements.txt

@@ -1,8 +1,9 @@
-nose==1.3.7
-zipp==0.5.0
-flake8==2.6.2
 coverage==4.5.4
 coveralls==1.0
-pep8==1.7.1
-pep8-naming==0.3.3
+flake8==2.6.2
+#flake8==3.8.4
+nose==1.3.7
 numpy==1.19.2
+pep8-naming==0.3.3
+pep8==1.7.1
+zipp==0.5.0