python-3-object-oriented-programming by Unknown

Author:Unknown
Language: rus
Format: epub
Tags: www.it-ebooks.info
Published: 2015-08-14T10:57:54+00:00

Python Object-oriented Shortcuts

Keyword arguments are also very useful when we need to accept arbitrary arguments to pass to a second function, but we don't know what those arguments will be. We saw this in action in Chapter 3, When Objects Are Alike, when we were building support for multiple inheritance. We can, of course, combine the variable argument and variable keyword argument syntax in one function call, and we can use normal positional and default arguments as well. The following example is somewhat contrived, but demonstrates the four types in action:

import shutil

import os.path

def augmented_move(target_folder, *filenames,

verbose=False, **specific):

'''Move all filenames into the target_folder, allowing

specific treatment of certain files.'''

def print_verbose(message, filename):

'''print the message only if verbose is enabled'''

if verbose:

print(message.format(filename))

for filename in filenames:

target_path = os.path.join(target_folder, filename)

if filename in specific:

if specific[filename] == 'ignore':

print_verbose("Ignoring {0}", filename)

elif specific[filename] == 'copy':

print_verbose("Copying {0}", filename)

shutil.copyfile(filename, target_path)

else:

print_verbose("Moving {0}", filename)

shutil.move(filename, target_path)

This example will process an arbitrary list of files. The first argument is a target folder, and the default behavior is to move all remaining non-keyword argument files into that folder. Then there is a keyword-only argument, verbose, which tells us whether to print information on each file processed. Finally, we can supply a dictionary containing actions to perform on specific filenames; the default behavior is to move the file, but if a valid string action has been specified in the keyword arguments, it can be ignored or copied instead. Notice the ordering of the parameters in the function; first the positional argument is specified, then the *filenames list, then any specific keyword-only arguments, and finally, a **specific dictionary to hold remaining keyword arguments.

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