share function argument between subsequent calls but not between class instances!

[Steven D'Aprano]

On Mon, 20 Feb 2006 08:52:09 +0000, Duncan Booth wrote:

> Ben Finney wrote:
> 
>> Duncan Booth <duncan.booth at invalid.invalid> writes:
>>> If you intend to only use the default some of the time, and at other
>>> times pass in a different list, then save the 'default' in the
>>> instance and use a special marker value to indicate when you intend
>>> the default to be used:
>> 
>> The most common idiom for such a marker is the None value.
>> 
> 
> Can you provide any firm evidence that using None is more common?


Yes, I wrote a quick and dirty script to roughly count the default
values in the Python 2.3 standard library. Here are my results:

$ python default_counter.py
185 .py source files were opened.
4437 function or method definitions were found.
These functions included at least 1228 arguments with default values.
529 or 4.307818e+01% used None as the default value.

So, roughly 40% of default values in the standard library are None. If I
cared enough (I don't) I would re-write the counter to analyse all the
default values. But by eye-balling the function lines, the impression I
get is that the remaining 60% of default values are divided unequally
between dozens of different defaults. Some random examples:

"rb", "", "Prompt: ", -1, 0, 1, 3, sys.maxint, (), [].

My gut-feeling would be, 40-odd percent None, 40-odd percent for small
ints (-1, 0, 1, ..?), the remainder split between everything else.

If anyone cares to look at my quick and dirty source code, it is attached
following my signature.


-- 
Steven.




* * * 

"""Rough and ready script to analyse the Python standard library 
and count function definitions that use None as a default argument.
"""

from __future__ import division
import os

location = "/usr/lib/python2.3/"

file_count = 0  # number of files successfully opened
func_count = 0  # number of function definitions
default_count = 0  # number of functions with a default value
none_count = 0  # number of functions with None as a default value

for name in os.listdir(location):
    if name.endswith(".py") and os.path.isfile(location+name):
        try:
            fp = file(location+name, "r")
        except IOError:
            continue
        file_count += 1
        lines = fp.readlines()
        fp.close()
        for line in lines:
            line = line.strip()
            if line.startswith("#"):
                continue
            elif line.startswith("def "):
                func_count += 1
                default_count += line.count("=")
                none_count += line.count("None")
                # if line.count("="): print line

# Report results found:

print "%d .py source files were opened." % file_count
print "%d function or method definitions were found." % func_count
print "These functions included at least %d arguments with default values." % default_count
print "%d or %e%% used None as the default value." % \
(none_count, none_count/default_count*100)