.NODE

The Bastion Module

The Bastion module, shown in Example 14-7, allows you to control how a given object is used. It can be used to pass objects from unrestricted parts of your application to code running in restricted mode.

To create a restricted instance, simply call the Bastion wrapper. By default, all instance variables are hidden, as well as all methods that start with an underscore.

Example 14-7. Using the Bastion Module
File: bastion-example-1.py

import Bastion

class Sample:
 value = 0

 def _set(self, value):
 self.value = value

 def setvalue(self, value):
 if 10 < value <= 20:
 self._set(value)
 else:
 raise ValueError, "illegal value"

 def getvalue(self):
 return self.value

#
# try it

s = Sample()
s._set(100) # cheat
print s.getvalue()

s = Bastion.Bastion(Sample())
s._set(100) # attempt to cheat
print s.getvalue()

100
Traceback (innermost last):
...
AttributeError: _set

You can control which functions to publish. In Example 14-8, the internal method can be called from outside, but the getvalue no longer works.

Example 14-8. Using the Bastion Module with a Non-Standard Filter
File: bastion-example-2.py

import Bastion

class Sample:
 value = 0

 def _set(self, value):
 self.value = value

 def setvalue(self, value):
 if 10 < value <= 20:
 self._set(value)
 else:
 raise ValueError, "illegal value"

 def getvalue(self):
 return self.value

#
# try it

def is_public(name):
 return name[:3] != "get"

s = Bastion.Bastion(Sample(), is_public)
s._set(100) # this works
print s.getvalue() # but not this

100
Traceback (innermost last):
...
AttributeError: getvalue

Core Modules

More Standard Modules

Threads and Processes

Data Representation

File Formats

Mail and News Message Processing

Network Protocols

Internationalization

Multimedia Modules

Data Storage

Tools and Utilities

Platform-Specific Modules

Implementation Support Modules

Other Modules





Python Standard Library
Python Standard Library (Nutshell Handbooks) with
ISBN: 0596000960
EAN: 2147483647
Year: 2000
Pages: 252
Authors: Fredrik Lundh
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