How to write verbose scripts

Steven D'Aprano steve at
Tue Sep 2 18:55:53 CEST 2008

I find myself writing command line tools in Python where I wish to 
include "verbose" output to stdout.

I start with a helper function:

def print_(obj, level=0):
    if _verbosity >= level:
        print obj

And then I end up with functions or methods looking like this:

def parrot(x)
    print_("precondition", level=2)
    print_("status is good...", level=1)
    print_("parrot is squawking strongly now", level=2)
    print_("squawk squawk squawk", level=3)
    print_("postcondition", level=1)
    return something

That often means that my functions end up with more message printing code 
than actual code. The whole thing seems messy and hard to manage for all 
but the smallest scripts.

Worst of all, sometimes the messages I wish to print may be expensive to 
compute, and I don't want to waste time computing them if they aren't 
going to be printed because the verbosity is too low. But nor do I wish 
to fill my code with this:

if _verbosity >= 3:
    x = calculate_complicated_thing()
    print_(x, level=3)

Is there a better way of doing this than the way I am going about it?


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