[Python-Dev] Does Zip Importer have to be Special? (original) (raw)

Phil Thompson phil at riverbankcomputing.com
Thu Jul 24 20:12:13 CEST 2014

On 24/07/2014 6:48 pm, Brett Cannon wrote:

On Thu Jul 24 2014 at 1:07:12 PM, Phil Thompson <phil at riverbankcomputing.com> wrote:

I have an importer for use in applications that embed an interpreter that does a similar job to the Zip importer (except that the storage is a C data structure rather than a .zip file). Just like the Zip importer I need to import my importer and add it to sys.pathhooks. However the earliest opportunity I have to do this is after the PyInitialize() call returns - but this is too late because some parts of the standard library have already needed to be imported.

My current workaround is to include a modified version of bootstrap.py as a frozen module that has the necessary steps added to the end of its install() function. The Zip importer doesn't have this problem because it gets special treatment - the call to its equivalent code is hard-coded and happens exactly when needed. What would help is a table of functions that were called where PyImportZipInit() is currently called. By default the only entry in the table would be PyImportZipInit. There would be a way of modifying the table, either like how PyImportFrozenModules is handled or how Inittab is handled. ...or if there is a better solution that I have missed that doesn't require a modified bootstrap.py. Basically you want a way to specify arguments into importlib.bootstrap.install() so that sys.pathhooks and sys.metapath were configurable instead of hard-coded (it could also be done just past importlib being installed, but that's a minor detail). Either way there is technically no reason not to allow for it, just lack of motivation since this would only come up for people who embed the interpreter AND have a custom importer which affects loading the stdlib as well (any reason you can't freeze the stdblib as a solution?).

Not really. I'd lose the compression my importer implements.

(Are there any problems with freezing packages rather than simple modules?)

We could go the route of some static array that people could modify. Another option would be to allow for the specification of a single function which is called just prior to importing the rest of the stdlib,

The problem with all of this is you are essentially asking for a hook to let you have code have access to the interpreter state before it is fully initialized. Zipimport and the various bits of code that get loaded during startup are special since they are coded to avoid touching anything that isn't ready to be used. So if we expose something that allows access prior to full initialization it would have to be documented as having no guarantees of interpreter state, etc. so we are not held to some API that makes future improvements difficult. IOW allowing for easy patching of Python is probably the best option I can think of. Would tweaking importlib.bootstrap.install() to accept specified values for sys.metapath and sys.pathhooks be enough so that you can change the call site for those functions?

My importer runs under PathFinder so it needs sys.path as well (and doesn't need sys.meta_path).

Phil

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