requests_additives.py

class TimeoutMixin:
    def send(self, *args, **kwargs):
        if hasattr(self, 'timeout') and 'timeout' not in kwargs:
            kwargs['timeout'] = self.timeout
        return super().send(*args, **kwargs)

# Use
import requests

class Session(TimeoutMixin, requests.Session):
    pass

session = Session()
session.timeout = 120
session.get('https://httpbin.org/get')