Answers for "how to use a requirements.txt file"

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)

install requirements.txt in pip command

note: yor should be on the same dir as requirements.txt file 

pip install -r requirements.txt

how to install requirements.txt

pip3 install -r requirements.txt

python requirements.txt

# to generate the requirements.txt file:
pip install pipreqs	# Install via teminal.
pipreqs path/to/project	# Generate requirements.txt file
# There is now a requirements.txt file in the project folder.
# to install a requirements.txt file:
pip install -r requirements.txt
# please leave a like ;)