2

I have a reporting function on my Web Application that has been subjected to Feature Creep -- instead of providing a PDF, it must now provide a .zip file that contains a variety of documents.

Generating the documents is fine. Adding documents to the Zipfile is the issue.

Until now, the various documents to be added to the archive have existed as a mix of cStringIO, StringIO or tempfile.SpooledTemporaryFile objects.

Digging into the zipfile library docs, it appears that the module's [write][1] function will only work with Strings or paths to physical files on the machine; it does not work with file-like objects.

Just to be clear: zipfile can read/write from a file-like object as the archive itself (zipfile.ZipFile), however when adding an element to the archive, the library only supports a pathname or raw string data.

I found an online blog posting suggesting a possible workaround, but I'm not eager to use it on my production machine. http://swl10.blogspot.com/2012/12/writing-stream-to-zipfile-in-python.html

Does anyone have other strategies for handling this? It looks like I have to either save everything to disk and take a hit on I/O , or handle everything as a string and take a hit on memory. Neither are ideal.

Dharman
  • 30,962
  • 25
  • 85
  • 135
Jonathan Vanasco
  • 15,111
  • 10
  • 48
  • 72
  • Do you have any particular reason to distrust the solution you linked? It looks solid to me - the hooks it adds to `os.stat` and `__builtin__.open` do absolutely nothing unless the virtual file class is passed. – GVH Mar 21 '14 at 20:36
  • I generally don't like monkeypatching things, and this monkeypatches std libraries. If I were just running an isolated script, I wouldn't care. This is part of a large web services project, and may be called from one of the async daemons. Even though that VirtualClass is required, I'm still a bit concerned. That concern could be unfounded, and I'd be happy to learn otherwise. Introducing code from a random blog post that monkeypatches `os` is something I'd rather have other people chime in on. – Jonathan Vanasco Mar 24 '14 at 14:28

1 Answers1

0

Use the solution you are referring to (using monkeypathing).

Regarding your concerns about monkeypathing thing not sounding solid enough: Do elaborate on how can be monkeypatched method used from other places.

Hooking in Python is no special magic. It means, that someone assigns alternative value/function to something, what is already defined. This has to be done by a line of code and has very limited scope.

In the example from the blog is the scope of monkeypatched os functions just the class ZipHooks.

Do not be afraid, that it would leak somewhere else without your knowledge or break complete system. Even other packages, importing your module with ZipHooks class would not have access to pathed stat and open unless they would use ZipHooks class or explicitly call stat_hook or open_hook from your package.

Jan Vlcinsky
  • 42,725
  • 12
  • 101
  • 98