Python Notes

1. Python Documentation

  • A reference guide can be found here

  • Full document can be found here.

2. Where is Python installed on Windows?

  1. Open a cmd prompt and execute the following:

    $ py --list-paths
    Sample Output
    Installed Pythons found by C:\WINDOWS\py.exe Launcher for Windows *


 -3.10-64       C:\Users\<user name>\AppData\Local\Programs\Python\Python310\python.exe
 -3.9-64        C:\Users\<user name>\AppData\Local\Programs\Python\Python39\python.exe

3. Python Linters

3.1. Ruff

  • Ruff is available as a Visual Studio Code Extension.

    1. Disable the following Extensions:

      1. Pylint - checks for errors, enforces a coding standard, looks for code smells, and can make suggestions about how the code could be refactored

      2. Pylance - the language server providing type checking and other features

    2. Enable the Ruff Extension

3.2. Pylint

  • To disable specific pylint message codes within a particular source file, add similar comments to the following at the top of the file.

    Expand for example pylint message codes 
    #region suppress pylint messages
# pylint: disable=broad-exception-caught
# pylint: disable=broad-exception-raised
# pylint: disable=global-statement
# pylint: disable=global-variable-undefined
# ppylint: disable=invalid-name
# pylint: disable=line-too-long
# pylint: disable=missing-class-docstring
# pylint: disable=missing-function-docstring
# pylint: disable=missing-class-docstring
# pylint: disable=multiple-statements
# pylint: disable=too-few-public-methods
# pylint: disable=too-many-branches
# pylint: disable=too-many-locals
# pylint: disable=too-many-instance-attributes
# pylint: disable=too-many-statements
# pylint: disable=trailing-whitespace
#endregion

4. How to Start Interactive Mode

  1. Open a cmd prompt and execute the py -3 command:

    C:\Users\<user_name>py -3  (1)
Python 3.10.4 (tags/v3.10.4:9d38120, Mar 23 2022, 23:13:41) [MSC v.1929 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> print("Hello")      (2)
Hello
>>> quit()              (3)
    1 Execute this command to start v3 of Python.
    2 Run a Python command.
    3 Quit the interactive shell.

5. Packages

  • Full document can be found here.

    • If the intention is to install a package into a venv, confirm that the venv is the current directory.

5.1. Install PIP

5.1.1. Install PIP on Linux

  1. Installer:

    sudo apt install python3-pip

5.2. List Packages

  1. Open a cmd prompt and execute one of the following:

    Windows
    py -3 -m pip list
    venv
    pip list

5.3. List Packages Location

  1. Open a cmd prompt and execute one of the following:

    Windows
    py -c "import site; print(site.getsitepackages())"
    Linux
    python3 -c "import site; print(site.getsitepackages())"

5.4. Install a Package

  1. Open a cmd prompt and execute one of the following:

    Windows
    py -3 -m pip install SomePackage
    Unix
    python -m pip install SomePackage
    venv
    pip install SomePackage

5.5. Upgrade a Package

  1. Open a cmd prompt and execute one of the following:

    py -3 -m pip install --upgrade SomePackage  (1)

pip install --upgrade SomePackage           (2)
    1 Upgrade SomePackage globally.
    2 Upgrade SomePackage in a venv.

5.6. Remove a Package

  1. Open a cmd prompt and execute one of the following:

    py -3 -m pip uninstall SomePackage    (1)

pip uninstall SomePackage             (2)
    1 Uninstall SomePackage globally.
    2 Uninstall SomePackage in a venv.

6. Python Virtual Environment (venv) on Windows

  • Full document can be found here.

6.1. Summary

  • A Python Virtual Environment is simply a folder containing a specific version of a Python interpreter bundled together with specific Python packages.

6.2. Create venv

  • Open a cmd window and run the following command:

    py -3 -m venv tutorial-env (1)
    1 This will create a venv folder named tutorial-env.

  • The previous step created a new venv folder named tutorial-env.

    Python-VENV

  • Within that new folder is an initial set of packages.

    Python-VENV-Default-Packages

6.3. Select venv

  • Now select the Python Interpreter within the new venv folder:

    1. Open the Command Palette via Ctrl+Shift+P and select the venv:

      Python-VENV-Select-Interpreter

  • Now in the lower right hand corner of the IDE, you’ll see that the venv is selected:

    Python-VENV-Selected

6.4. Override the Venv Python with a System Python

  1. Identify a system Python. Open a cmd prompt and execute the following:

    py --list-paths
    Sample Output
    Installed Pythons found by C:\WINDOWS\py.exe Launcher for Windows *


 -3.10-64       C:\Users\<user name>\AppData\Local\Programs\Python\Python310\python.exe
 -3.9-64        C:\Users\<user name>\AppData\Local\Programs\Python\Python39\python.exe

    In this example, two system Python executables were identified.

  2. Create the soft link

    1. The Python interpreter in the venv will be deleted in a later step so confirm that it is not currently selected.

      If not sure run the deactivate script:
      .\script\deactivate

    2. Launch a CMD window

    3. cd into the venv folder

      Example
      cd C:\Users\<user name>\source\repos\GitLab\repo-python\tutorial-env

    4. Delete the current python.exe from the Scripts folder

      del .\Scripts\python.exe

    5. Create a link to the system Python identified in an earlier step.

      mklink LinkName TargetFilePath
      Example
      mklink .\Scripts\python.exe C:\Users\<user name>\AppData\Local\Programs\Python\Python310\python.exe

New-Item -Path ".\Scripts\python.exe" -ItemType SymbolicLink -Value "C:\Users\mattosd\AppData\Local\Programs\Python\Python310\python.exe"

  3. Copy DLL

    • The python3xx.dll will need to be copied into the venv’s Scripts folder:

      Example
      copy "C:\Users\<user name>\AppData\Local\Programs\Python\Python310\python310.dll" .\scripts

7. GUI TKinter

  • The Tkinter library is built into Python

  • A Tkinter Tutorial can be found here.

7.1. Pygubu - TKinter Visual Design Tool

  • Pygubu is a RAD tool which can be found here.

7.1.1. Install

  • py -3 -m pip install pygubu

  • py -3 -m pip install pygubu-designer

    • Execute

  • Open a CMD prompt to: c:\Users\<user_name>\AppData\Local\Programs\Python\Python310\Scripts

  • Execute: pygubu-designer.exe

8. DB Access

8.1. PyODBC

  1. Install pyodbc

    py -3 -m pip install pyodbc

8.1.1. MSSQL Server

  1. Confirm an existing ODBC Driver for Sql Server driver via the ODBC tool. The following indicates that version 17 of the driver is installed:

    Python-DB-ODBC-Driver-Exists

  2. If the driver doesn’t exist or is an older version, install ODBC Driver for SQL Server:

    • Download installer from here .

  3. Install the Python driver:

    py -3 -m pip install pymssql

  4. Code example:

    import pyodbc
# Some other example server values are
# server = 'localhost\sqlexpress' # for a named instance
# server = 'myserver,port' # to specify an alternate port
server = 'tcp:myserver.database.windows.net'
database = 'mydb'
username = 'myusername'
password = 'mypassword'
cnxn = pyodbc.connect('DRIVER={ODBC Driver 17 for SQL Server};SERVER='+server+';DATABASE='+database+';UID='+username+';PWD='+ password)  (1)
cursor = cnxn.cursor()
    1 Note that version 17 of driver is specified in the connection string.