When you use python file as module there is no need always check if package is installed but it is still useful for scripts.
if __name__ == '__main__':
try:
import requests
except ImportError:
print("To use this module you need 'requests' module")
t = input('Install requests? y/n: ')
if t == 'y':
import pip
pip.main(['install', 'requests'])
import requests
import os
import sys
pass
else:
import os
import sys
print('Some functionality can be unavailable.')
else:
import requests
import os
import sys