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Python Library Reference |  |
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Python Library Reference | |
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This module contains the RExec class, which supports r_eval(), r_execfile(), r_exec(), and r_import() methods, which are restricted versions of the standard Python functions eval(), execfile() and the exec and import statements. Code executed in this restricted environment will only have access to modules and functions that are deemed safe; you can subclass RExec to add or remove capabilities as desired.
Note: The RExec class can prevent code from performing unsafe operations like reading or writing disk files, or using TCP/IP sockets. However, it does not protect against code using extremely large amounts of memory or CPU time.
hooks is an instance of the RHooks class or a subclass of it.
If it is omitted or None, the default RHooks class is
instantiated.
Whenever the rexec module searches for a module (even a
built-in one) or reads a module's code, it doesn't actually go out to
the file system itself. Rather, it calls methods of an RHooks
instance that was passed to or created by its constructor. (Actually,
the RExec object doesn't make these calls -- they are made by
a module loader object that's part of the RExec object. This
allows another level of flexibility, e.g. using packages.)
By providing an alternate RHooks object, we can control the file system accesses made to import a module, without changing the actual algorithm that controls the order in which those accesses are made. For instance, we could substitute an RHooks object that passes all filesystem requests to a file server elsewhere, via some RPC mechanism such as ILU. Grail's applet loader uses this to support importing applets from a URL for a directory.
If verbose is true, additional debugging output may be sent to standard output.
It is important to be aware that code running in a restricted
environment can still call the sys.exit() function. To
disallow restricted code from exiting the interpreter, always protect
calls that cause restricted code to run with a
try/except statement that catches the
SystemExit exception. Removing the sys.exit()
function from the restricted environment is not sufficient -- the
restricted code could still use raise SystemExit. Removing
SystemExit is not a reasonable option; some library code
makes use of this and would break were it not available.
See Also:
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Python Library Reference | |
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