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227 lines
8.5 KiB
Python
227 lines
8.5 KiB
Python
###
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# Copyright (c) 2005, Jeremiah Fincher
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# All rights reserved.
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#
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# Redistribution and use in source and binary forms, with or without
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# modification, are permitted provided that the following conditions are met:
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#
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# * Redistributions of source code must retain the above copyright notice,
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# this list of conditions, and the following disclaimer.
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# * Redistributions in binary form must reproduce the above copyright notice,
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# this list of conditions, and the following disclaimer in the
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# documentation and/or other materials provided with the distribution.
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# * Neither the name of the author of this software nor the name of
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# contributors to this software may be used to endorse or promote products
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# derived from this software without specific prior written consent.
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#
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# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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# POSSIBILITY OF SUCH DAMAGE.
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###
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"""
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Defines a Transaction class for multi-file transactions.
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"""
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import os
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import shutil
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import os.path
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import error
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import python
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import file as File
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# 'txn' is used as an abbreviation for 'transaction' in the following source.
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class FailedAcquisition(error.Error):
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def __init__(self, txnDir, e=None):
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self.txnDir = txnDir
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msg = 'Could not acquire transaction directory: %s.' % self.txnDir
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error.Error.__init__(self, msg, e)
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class InProgress(error.Error):
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def __init__(self, inProgress, e=None):
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self.inProgress = inProgress
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msg = 'Transaction appears to be in progress already: %s exists.' % \
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self.inProgress
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error.Error.__init__(self, msg, e)
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class TransactionMixin(python.Object):
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JOURNAL = 'journal'
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ORIGINALS = 'originals'
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INPROGRESS = '.inProgress'
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REPLACEMENTS = 'replacements'
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# expects a self.dir. used by Transaction and Rollback.
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def __init__(self, txnDir):
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self.txnDir = txnDir
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self.dir = self.txnDir + self.INPROGRESS
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self._journalName = self.dirize(self.JOURNAL)
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def escape(self, filename):
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return os.path.abspath(filename)[1:]
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def dirize(self, *args):
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return os.path.join(self.dir, *args)
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def _original(self, filename):
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return self.dirize(self.ORIGINALS, self.escape(filename))
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def _replacement(self, filename):
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return self.dirize(self.REPLACEMENTS, self.escape(filename))
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def _checkCwd(self):
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expected = File.contents(self.dirize('cwd'))
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if os.getcwd() != expected:
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raise InvalidCwd(expected)
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def _journalCommands(self):
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journal = open(self._journalName)
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for line in journal:
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line = line.rstrip('\n')
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(command, rest) = line.split(None, 1)
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args = rest.split()
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yield (command, args)
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class Transaction(TransactionMixin):
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# XXX Transaction needs to be made threadsafe.
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def __init__(self, *args, **kwargs):
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"""Transaction(txnDir) -> None
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txnDir is the directory that will hold the transaction's working files
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and such. If it can't be renamed, there is probably an active
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transaction.
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"""
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TransactionMixin.__init__(self, *args, **kwargs)
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if os.path.exists(self.dir):
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raise InProgress(self.dir)
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if not os.path.exists(self.txnDir):
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raise FailedAcquisition(self.txnDir)
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try:
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os.rename(self.txnDir, self.dir)
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except EnvironmentError, e:
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raise FailedAcquisition(self.txnDir, e)
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os.mkdir(self.dirize(self.ORIGINALS))
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os.mkdir(self.dirize(self.REPLACEMENTS))
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self._journal = open(self._journalName, 'a')
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cwd = open(self.dirize('cwd'), 'w')
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cwd.write(os.getcwd())
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cwd.close()
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def _journalCommand(self, command, *args):
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File.writeLine(self._journal,
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'%s %s' % (command, ' '.join(map(str, args))))
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self._journal.flush()
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def _makeOriginal(self, filename):
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File.copy(filename, self._original(filename))
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# XXX There needs to be a way, given a transaction, to get a
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# "sub-transaction", which:
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#
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# 1. Doesn't try to grab the txnDir and move it, but instead is just
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# given the actual directory being used and uses that.
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# 2. Acquires the lock of the original transaction, only releasing it
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# when its .commit method is called (assuming Transaction is
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# threadsafe).
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# 3. Has a no-op .commit method (i.e., doesn't commit).
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#
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# This is so that, for instance, an object with an active Transaction
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# can give other objects a Transaction-ish object without worrying that
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# the transaction will be committed, while still allowing those objects
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# to work properly with real transactions (i.e., they still call
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# as they would on a normal Transaction, it just has no effect with a
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# sub-transaction).
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# The method that returns a subtransaction should be called "child."
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def child(self):
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raise NotImplementedError
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# XXX create, replace, etc. return file objects. This class should keep a
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# list of such file descriptors and only allow a commit if all of them
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# are closed. Trying to commit with open file objects should raise an
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# exception.
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def create(self, filename):
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"""
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Returns a file object for a filename that should be created (with
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the contents as they were written to the filename) when the transaction
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is committed.
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"""
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raise NotImplementedError # XXX.
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def mkdir(self, filename):
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raise NotImplementedError # XXX
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def delete(self, filename):
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raise NotImplementedError # XXX
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def replace(self, filename):
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"""
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Returns a file object for a filename that should be replaced by the
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contents written to the file object when the transaction is committed.
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"""
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self._checkCwd()
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self._makeOriginal(filename)
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self._journalCommand('replace', filename)
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return File.open(self._replacement(filename))
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def append(self, filename):
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self._checkCwd()
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length = os.stat(filename).st_size
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self._journalCommand('append', filename, length)
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replacement = self._replacement(filename)
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File.copy(filename, replacement)
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return open(replacement, 'a')
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def commit(self, removeWhenComplete=True):
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self._journal.close()
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self._checkCwd()
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File.touch(self.dirize('commit'))
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for (command, args) in self._journalCommands():
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methodName = 'commit%s' % command.capitalize()
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getattr(self, methodName)(*args)
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File.touch(self.dirize('committed'))
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if removeWhenComplete:
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shutil.rmtree(self.dir)
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def commitReplace(self, filename):
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shutil.copy(self._replacement(filename), filename)
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def commitAppend(self, filename, length):
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shutil.copy(self._replacement(filename), filename)
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# XXX need to be able to rename files transactionally. (hard; especially
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# with renames that depend on one another. It might be easier to do
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# rename separate from relocate.)
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class Rollback(TransactionMixin):
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def rollback(self, removeWhenComplete=True):
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self._checkCwd()
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if not os.path.exists(self.dirize('commit')):
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return # No action taken; commit hadn't begun.
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for (command, args) in self._journalCommands():
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methodName = 'rollback%s' % command.capitalize()
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getattr(self, methodName)(*args)
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if removeWhenComplete:
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shutil.rmtree(self.dir)
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def rollbackReplace(self, filename):
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shutil.copy(self._original(filename), filename)
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def rollbackAppend(self, filename, length):
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fd = open(filename, 'a')
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fd.truncate(int(length))
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fd.close()
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# vim:set shiftwidth=4 softtabstop=8 expandtab textwidth=78:
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