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command.py

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#!/usr/bin/env python

# -*- coding: utf-8 -*-

"""

*TL;DR80

Encapsulates all information needed to perform an action or trigger an event.

"""

from __future__ import print_function

import os

from os.path import lexists

class MoveFileCommand(object):

def __init__(self, src, dest):

self.src = src

self.dest = dest

def execute(self):

self.rename(self.src, self.dest)

def undo(self):

self.rename(self.dest, self.src)

def rename(self, src, dest):

print(u"renaming %s to %s" % (src, dest))

os.rename(src, dest)

def main():

command_stack = []

# commands are just pushed into the command stack

command_stack.append(MoveFileCommand('foo.txt', 'bar.txt'))

command_stack.append(MoveFileCommand('bar.txt', 'baz.txt'))

# verify that none of the target files exist

assert(not lexists("foo.txt"))

assert(not lexists("bar.txt"))

assert(not lexists("baz.txt"))

try:

with open("foo.txt", "w"): # Creating the file

pass

# they can be executed later on

for cmd in command_stack:

cmd.execute()

# and can also be undone at will

for cmd in reversed(command_stack):

cmd.undo()

finally:

os.unlink("foo.txt")

if __name__ == "__main__":

main()

### OUTPUT ###

# renaming foo.txt to bar.txt

# renaming bar.txt to baz.txt

# renaming baz.txt to bar.txt

# renaming bar.txt to foo.txt