Python

Check out this cheatsheet: python cheatsheet

Virtual environments

To activate an existing virtual environment (venv) use the activate.bat. If project is at c:\someproject and has venv folder at c:\someproject\someVenv then usually call: someVenv\scripts\activate.bat

pip list lists the actual packages in the venv

// navigate to project folder  
cd c:\someproject
  
// create a new directory 'project-36'  
mkdir project-36  
  
// change currenct directory to 'project-36'  
cd .\project-36  
  
// create a virtual environment named 'venv', feel free to name it anything you like. -p Location is optional but makes sure to use a specific python version.
virtualenv venv -p C:\Python\Python36\python.exe  

// activate the virtual environment
.\venv\Scripts\activate

// check the python version
python --version

// list all packages installed by default
pip list

// deactivate the virtual environment
deactivate

See also pipx for managing global packages that are not project-bound.

Taking arguments

Argparse has all the functionality one could want. See: docs.python.org

Stopping execution

On windows (and sometimes linux) cancelling python in the terminal can be tricky since io operations can ignore ctrl+c and similar commands. ctrl+break seems to work though and on thinkpad laptops is done with ctrl+fn+b due to the lacking break button.

Project templates

Cookiecutter allows setting up new projects from templates.

Notes on useful language elements, functions etc.

List comprehension (with condition):

fruits = ["apple", "banana", "cherry", "kiwi", "mango"]
newlist = [x for x in fruits if "a" in x]

Dict comprehensions and enumeration:

fruits = ["apple", "banana", "cherry", "kiwi", "mango"]
newDict = {fruit: index for index, fruit in enumerate(fruits)]

Sort with key:

numLetters = [(1,b),(2,a),(3,d)]
sortedByFirst = numLetters.sort(key=itemgetter(0))
sortedByFirstThenSecond = numLetters.sort(key=itemgetter(0,1))
reverseSortedByFirst = numLetters.sort(key=itemgetter(0), reverse=True)

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