Popular recipes tagged "contextmanager" but not "with"

Context Manager for an Arbitrary Number of Files in Python (Python)

2017-03-13T13:27:50-07:00

Python recipe 580763 by Alfe (contextmanager, file, open). Revision 2.

The pattern using with together with open() to automatically close a file after leaving the context is well known. To open a fixed number you can simply nest these statements or use the comma notation. For having a context which represents an arbitrary number of open files you can use the ExitStack class, but only for Python 3.3+.

For other Python versions I'm using the following class which I named Files. The presented implementation is only for reading files (for keeping it clear). Extending it for having various file modes should not pose a problem.

Use PDFWriter with context manager support (Python)

2013-12-16T21:43:27-08:00

Python recipe 578790 by Vasudev Ram (contextmanager, context_manager, pdf, python, reportlab, with_statement, xtopdf).

PDFWriter - a core class of the xtopdf toolkit - can now be used with a Python context manager, a.k.a. the Python with statement.

Code example below. More details here:

http://jugad2.blogspot.in/2013/12/xtopdf-pdfwriter-now-has-context.html

Wrap any iterable context manager so it closes when consumed (Python)

2012-11-19T20:10:35-08:00

Python recipe 578342 by Andrew Barnert (contextmanager, context_manager, generator, iterable, iterator, with_statement).

There are a few types in Python—most notably, files—that are both iterators and context managers. For trivial cases, these features are easy to use together, but as soon as you need to use the iterator lazily or asynchronously, a with statement won't help. That's where this recipe comes in handy:

send_async(with_iter(open(path, 'r')))

This also allows you to "forward" closing for a wrapped iterator, so closing the outer iterator also closes the inner one:

sync_async(line.upper() for line in with_iter(open(path, 'r')))

Context manager to atomically replace a file (Python)

2012-06-17T12:09:49-07:00

Python recipe 578166 by Oren Tirosh (atomic, contextmanager, file, replace). Revision 3.

This context manager ensures that a file's content is either replaced atomically with new contents or left unchanged. An exception or other error will not leave it empty or with partial content.

Handle exit context manager (Python)

2014-08-01T08:28:07-07:00

Python recipe 577997 by Giampaolo Rodolà (atexit, contextlib, contextmanager, exit, python, python3, shutdown, sigint, signal, sigterm). Revision 23.

A context manager which properly handles SIGTERM (SystemExit) and SIGINT (KeyboardInterrupt) signals, registering a function which is always guaranteed to be called on interpreter exit. Also, it makes sure to execute previously registered functions as well (if any).

CleanupManager for with statements (Python)

2011-12-18T07:20:46-08:00

Python recipe 577981 by Nick Coghlan (contextmanager, context_manager). Revision 5.

Inspired by unittest.TestCase.addCleanup(), CleanupManager provides a means to programmatically add resources to be cleaned up when leaving a with statement. This makes it easy to use with optional resources, and those derived from sequences of inputs.

An more powerful version of this recipe with a few additional features is published under the name ContextStack as part of the contextlib2 module: http://contextlib2.readthedocs.org

This recipe is based on a suggestion originally posted by Nikolaus Rath at http://bugs.python.org/issue13585

Context manager for low-level redirection of stdout/stderr (Python)

2012-01-26T02:14:25-08:00

Python recipe 577564 by Greg Haskins (contextmanager, context_manager, f2py, fortran, python, redirect, stdout). Revision 3.

This context manager provides a convenient, Pythonic way to temporarily replace the file descriptors of stdout and stderr, redirecting to either os.devnull or files of your choosing. Swapping the C-level file descriptors is required when suppressing output from compiled extension modules, such as those built using F2PY. It functions equally well for pure-Python code. UPDATE: (see below).

Simple lock-queue via Memcached (Python)

2008-11-19T01:32:07-08:00

Python recipe 576567 by Tal Einat (concurrency, contextmanager, lock, locking, memcache, memcached, queue).

A simple lock-queue (FIFO) context manager implemented with Memcached.

In essence this is a normal lock, where the requests to acquire the lock are granted in the order in which they were originally made. Note that requests to acquire the lock are always blocking.