How to write create random username and password selenium python

how to i can write issue create random username password and select dropdown with selenium python ?

My code select dropdown:

self.find_element_by_xpath(randint(0, len("//*[@id='shop_delivery_delivery_id']") + 1))

and i have to error:

Traceback (most recent call last):
self.find_element_by_xpath(randint(0, len("//*[@id='shop_delivery_delivery_id']") + 1))
AttributeError: type object 'CreateDeliveryMode' has no attribute 'find_element_by_xpath'

I do not know why Please tell me how to write. Thank you Ps.I'm fairly new to python and selenium