Pass generator expression to str.join() instead of list / tuple throughout code base

[Chris Jerdonek]

In many places throughout Django's code base, a list or tuple is passed to str.join() when a generator expression would suffice. For example, instead of ', '.join([self.quote_name(field.column) for field in fields]) one can do ', '.join(self.quote_name(field.column) for field in fields). This eliminates an unneeded list creation. Many (but not all) examples can be found by searching the code base for .join([.

[Mariusz Felisiak]

A list comprehension is preferable here as str.join() converts to list internally anyway. It is better performance to provide a list up front.

• ​https://stackoverflow.com/questions/9060653/list-comprehension-without-in-python/9061024#9061024
• ​https://github.com/adamchainz/flake8-comprehensions/issues/156