Answers for "how to write requirements.txt"

python requirements.txt

pip freeze #view requirements to be created (best done in virtual env)
pip freeze > requirements.txt #create requirements.txt (best done in virtual env)
pip install -r requirements.txt #install requirements.txt (best done in virtual env)

how to generate requirements.txt django

For Unix families: pip3 freeze > requirements.txt
For Windos: pip freeze > requirements.txt

how to have requirement file in python for libs

pip3 freeze > requirements.txt