Here's the README.txt:
Python Libraries
The Python Libraries Product provides support for collections of restricted Python code. A Python Library is similar to a Folder full of Python-based Scripts, except that the functions in the Library are more like ordinary Python functions than Scripts, and a single persistent global variable namespace is shared among the functions in the Library.
A Library obeys the same security restrictions, and has access to the same set of modules, as a Script. Libraries are *not* very much like Python modules or packages, except in that they both are convenient places to keep groups of functions. You cannot import a Library, define Python classes in one, or use the 'print' statement outside of function definitions.
When changes to a Library are saved, its source code is executed. This process, known as "Library initialization", also occurs whenever the Library is loaded into memory from the ZODB. Global variables defined during initialization are divided into three groups, depending on the kind of value to which they refer: functions, simple data, and modules. There is one additional global variable, named 'Library', that is defined both during initialization and function evaluation, and which cannot be deleted or rebound. It refers to the Library object itself.
Functions are made available to other Zope code as Library attributes. A function 'do_it' contained in the Library located at '/foo/myLib' may be called by a TALES expression such as "here/foo/myLib/do_it" or the Python expression "context.foo.myLib.do_it()". Function names that conflict with methods of the Library object are syntax errors. A Library's functions are not published by default, which means that they cannot be accessed by URL through ZPublisher. There is a Library method 'pl_publish()' that can be used to explicitly publish a function.
Simple data includes Python built-in types such as numbers, strings, lists, and dictionaries. Variables with simple data are persistent, and their value is retained even when the Library is changed or reloaded, although the execution of the code can remove or overwrite them. These variables are not visible to other Zope objects.
Modules are imported Python modules. These are not visible to other Zope objects, and do not persist -- they are re-imported each time the Library is changed or loaded.
Unlike Scripts, Libraries do not have a Bindings tab. In order to access context objects, such as the Library's container, the root Zope object, or the authenticated user, functions must use a global variable created by a call to the 'pl_bind()' method of the Library. This method takes two arguments: a variable name, and a TALES expression. The TALES expression will be evaluated the first time that the variable is used in each call to a Library function, and the value will be cached for subsequent uses within the same call. For example, examine the following snippet of Library code:
Library.pl_bind('user', 'user')
Library.pl_bind('thingy', 'here/thingy | nothing')
def f():
if user.has_role('Authenticated') and thingy is not None:
print user, thingy
return printedWhen the function 'f' is called, the 'user' and 'thingy' variables will be evaluated in its first line, and the values will be reused in the second line, if the condition is true. If 'f' is called again, in the same request or not, the bound variables will be re-evaluated. Bound variables are not available during Library initialization, since they are unlikely to evaluate meaningfully when a Library is loaded from the ZODB.
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