advanced string formatting vs template strings

This is old but it is worth mentioning that one great advantage of using Template Strings is that it is safe when you are accepting the template from un-trusted source. This can be from a configuration file for instance.

Here is an example from this article:

CONFIG = {"SECRET_KEY": "super secret key"}

class Event:
    def __init__(self, id_, level, message):
        self.id_ = id_
        self.level = level
        self.message = message

def format_event(format_string, event):
    return format_string.format(event=event)


# user supplied template
inp = "{event.__init__.__globals__[CONFIG][SECRET_KEY]}"

event = Event(1234, "foo", "boo")
print(format_event(inp, event))

output:

super secret key

Adding to the other answers: one advantage of template strings vs. format strings is that often, the characters {} are more likely to naturally occur in a piece of text than $foo or ${foo} (e.g. when generating source code). That means that with templates, you need to spend less effort in escaping these occurrences of proper text.