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Python Execution in Special Dynamic Namespaces
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$Id$

  >>> from cybertools.util import namespace


A Very Restricted Basic Namespace
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  >>> minimal = namespace.BaseNamespace()

We

  >>> code = """
  ... print 'Hello'
  ... # a comment
  ... print dir('')
  ... print '__builtins__:', __builtins__
  ... output('something')
  ... a = 'a is a variable'
  ... if a:
  ...     print a
  ... """
  >>> exec code in minimal
  Hello
  ['__add__', ..., 'zfill']
  __builtins__: {}
  something
  a is a variable

Assignments in code executed in a namespace may be accessed as attributes
of the namespace later.

  >>> minimal.a
  'a is a variable'

By setting the ``__builtins__`` mapping to an empty dictionary the minimal
namespace provides a secure restricted execution environment.

  >>> exec "import os" in minimal
  Traceback (most recent call last):
  ...
  ImportError: __import__ not found

  >>> exec "f = open('dummy.txt', 'w')" in minimal
  Traceback (most recent call last):
  ...
  NameError: open


A Namespace Automatically Generating Symbols
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  >>> auto = namespace.AutoNamespace()

  >>> exec "print something" in auto
  something

  >>> auto.something
  <Symbol 'something'>