Next: 4.7.2 Keyword Arguments Up: 4.7 More on Defining Previous: 4.7 More on Defining

---

4.7.1 Default Argument Values

The most useful form is to specify a default value for one or more arguments. This creates a function that can be called with fewer arguments than it is defined, e.g.

    def ask_ok(prompt, retries=4, complaint='Yes or no, please!'):
        while 1:
            ok = raw_input(prompt)
            if ok in ('y', 'ye', 'yes'): return 1
            if ok in ('n', 'no', 'nop', 'nope'): return 0
            retries = retries - 1
            if retries < 0: raise IOError, 'refusenik user'
            print complaint

This function can be called either like this: ask_ok('Do you really want to quit?') or like this: ask_ok('OK to overwrite the file?', 2).

The default values are evaluated at the point of function definition in the defining scope, so that e.g.

    i = 5
    def f(arg = i): print arg
    i = 6
    f()

will print 5.