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def EnsureDefinition(name, definition, target=__builtins__.__dict__):
   
"""
    EnsureDefinition(name, definition, target)

    Ensure that a name exists in the given target namespace (a dictionary). If
    it does exist, do nothing. If it doesn't, execute the definition in the
    target.
    """

   
print 'Checking for %s in target...' % name,
   
if target.has_key(name):
       
print 'found.'
   
else:
       
print 'not found! Defining with %s' % definition
       
exec definition in target

EnsureDefinition('False','False = 0')
EnsureDefinition('True','True = not False')
EnsureDefinition('bool','''
def bool(x):
    if x:
        return True
    else:
        return False
'''


# Output for Python version < 2.2.1:
#
# Checking for False in target... not found! Defining with False = 0
# Checking for True in target... not found! Defining with True = not False
# Checking for bool in target... not found! Defining with def bool(x):
#     if x:
#         return True
#     else:
#         return False

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