import re
key_to_remove = r'sort_by'
rx = r'[?&]{0}=[^&]*$|(?<=[?&]){0}=[^&]*&'.format(key_to_remove)
tests = ['?sort_by=name&role=user','?gender=male&sort_by=name_desc&role=user','?sort_by=name','?age=24&sort_by=fullname&gender=male','?age=24&sort_by=fullname']
for test in tests:
print(test + " => " + re.sub(rx, "", test))
aW1wb3J0IHJlCmtleV90b19yZW1vdmUgPSByJ3NvcnRfYnknCnJ4ID0gcidbPyZdezB9PVteJl0qJHwoPzw9Wz8mXSl7MH09W14mXSomJy5mb3JtYXQoa2V5X3RvX3JlbW92ZSkKdGVzdHMgPSBbJz9zb3J0X2J5PW5hbWUmcm9sZT11c2VyJywnP2dlbmRlcj1tYWxlJnNvcnRfYnk9bmFtZV9kZXNjJnJvbGU9dXNlcicsJz9zb3J0X2J5PW5hbWUnLCc/YWdlPTI0JnNvcnRfYnk9ZnVsbG5hbWUmZ2VuZGVyPW1hbGUnLCc/YWdlPTI0JnNvcnRfYnk9ZnVsbG5hbWUnXQpmb3IgdGVzdCBpbiB0ZXN0czoKCXByaW50KHRlc3QgKyAiID0+ICIgKyByZS5zdWIocngsICIiLCB0ZXN0KSk=