8.3: Another Example
- Page ID
- 15462
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Here’s a version of increment
(from Section 16.3) rewritten as a method:
# inside class Time: def increment(self, seconds): seconds += self.time_to_int() return int_to_time(seconds)
This version assumes that time_to_int
is written as a method, as in Exercise 17.2.1. Also, note that it is a pure function, not a modifier.
Here’s how you would invoke increment
:
>>> start.print_time() 09:45:00 >>> end = start.increment(1337) >>> end.print_time() 10:07:17
The subject, start
, gets assigned to the first parameter, self
. The argument, 1337
, gets assigned to the second parameter, seconds
.
This mechanism can be confusing, especially if you make an error. For example, if you invoke increment
with two arguments, you get:
>>> end = start.increment(1337, 460) TypeError: increment() takes exactly 2 arguments (3 given)
The error message is initially confusing, because there are only two arguments in parentheses. But the subject is also considered an argument, so all together that’s three.