Decorator in python - explanation needed -

Decorator in python - explanation needed -

i new python , cant understand decorators concept. trying implement 2 decorators, one, nonnegative assumes arbitrarily long list of integer arguments , throws exception if less 0, , another, allcaps, assumes arbitrarily long list of string arguments, , capitalizes them. then, write simple function test each, wrap it, , demonstrate each decorator works.

i have started , have come point.

#!/usr/local/bin/python2.7 def nonnegative(inputs): in inputs: if i<0: raise exception def allcaps(inputs2): in inputs2: = i.upper() print def inputs def inputs2(): inputfile = open ("input.txt") sentence = inputfile.readlines() words = (sentence[0].split()) homecoming words nonnegative(inputs)

i grateful if can explain me concept of decorators. tried understand couldn't.

think of decorator function wraps function.

in math might have function f(x). if wrap decorator g have g(f(x)).

in python representation is

@function_g def function_f(): pass

here's example:

def entryexit(f): def new_f(): print "entering", f.__name__ f() print "exited", f.__name__ homecoming new_f @entryexit def func1(): print "inside func1()"

you see define function extryexit returns wrapped function (and hence takes function input). wraps function within of new_f.

by wrapping function decorator, func1 transforms from

def func1(): print "inside func1()"

to

def func1(f): print "entering", f.__name__ print "inside func1()" print "exited", f.__name__

you can write class define decorator, function decorators less verbose in opinion.

you can read more decorators this first-class intro here.

python decorator