import abc
import os
history = []
class Command(object):
"""The command interface."""
__metaclass__ = abc.ABCMeta
@abc.abstractmethod
def execute(self):
"""Method to execute the command."""
pass
@abc.abstractmethod
def undo(self):
"""A method to undo the command."""
pass
class LsCommand(Command):
"""Concrete command that emulates ls unix command behavior."""
def __init__(self, receiver):
self.receiver = receiver
def execute(self):
"""The command delegates the call to its receiver."""
self.receiver.show_current_dir()
def undo(self):
"""Can not undo ls command."""
pass
class LsReceiver(object):
def show_current_dir(self):
"""The receiver knows how to execute the command."""
cur_dir = './'
filenames = []
for filename in os.listdir(cur_dir):
if os.path.isfile(os.path.join(cur_dir, filename)):
filenames.append(filename)
print('Content of dir: ', ' '.join(filenames))
class TouchCommand(Command):
"""Concrete command that emulates touch unix command
behavior."""
def __init__(self, receiver):
self.receiver = receiver
def execute(self):
self.receiver.create_file()
def undo(self):
self.receiver.delete_file()
class TouchReceiver(object):
def __init__(self, filename):
self.filename = filename
def create_file(self):
"""Actual implementation of unix touch command."""
with open(self.filename, 'a'):
os.utime(self.filename, None)
def delete_file(self):
"""Undo unix touch command. Here we simply delete the file."""
os.remove(self.filename)
class RmCommand(Command):
"""Concrete command that emulates rm unix command behavior."""
def __init__(self, receiver):
self.receiver = receiver
def execute(self):
self.receiver.delete_file()
def undo(self):
self.receiver.undo()
class RmReceiver(object):
def __init__(self, filename):
self.filename = filename
self.backup_name = None
def delete_file(self):
"""Deletes file with creating backup to restore it in undo
method."""
self.backup_name = '.' + self.filename
os.rename(self.filename, self.backup_name)
def undo(self):
"""Restores the deleted file."""
original_name = self.backup_name[1:]
os.rename(self.backup_name, original_name)
self.backup_name = None
class Invoker(object):
def __init__(self, create_file_commands, delete_file_commands):
self.create_file_commands = create_file_commands
self.delete_file_commands = delete_file_commands
self.history = []
def create_file(self):
print('Creating file...')
for command in self.create_file_commands:
command.execute()
self.history.append(command)
print('File created.\n')
def delete_file(self):
print('Deleting file...')
for command in self.delete_file_commands:
command.execute()
self.history.append(command)
print('File deleted.\n')
def undo_all(self):
print('Undo all...')
for command in reversed(self.history):
command.undo()
print('Undo all finished.')
if __name__ == '__main__':
# Client
# List files in current directory
ls_receiver = LsReceiver()
ls_command = LsCommand(ls_receiver)
# Create a file
touch_receiver = TouchReceiver('test_file')
touch_command = TouchCommand(touch_receiver)
# Delete created file
rm_receiver = RmReceiver('test_file')
rm_command = RmCommand(rm_receiver)
create_file_commands = [ls_command, touch_command, ls_command]
delete_file_commands = [ls_command, rm_command, ls_command]
invoker = Invoker(create_file_commands, delete_file_commands)
invoker.create_file()
invoker.delete_file()
invoker.undo_all()
