Variable in xpath locator?

Question

Python

Good afternoon, there is such a serial_number variable that takes on a certain value
if you search for an element in this way:

find_serial_number = browser.find_element_by_xpath(".//*[contains(text(),'sn-12345']")

then everything works, but if you use a variable, then such an element is not found, I tried it in two ways

find_serial_number = browser.find_element_by_xpath(".//*[contains(text(),'sn-{0}'][' + serial_number']"

find_serial_number = browser.find_element_by_xpath(".//*[contains(text(),'sn-{0}'].format(serial_number)")

Answer 1

find_serial_number = browser.find_element_by_xpath(".//*[contains(text(),'"+serial_number+"')]")