Pearu Peterson pearu at cens.ioc.ee
Sat Dec 30 19:56:00 EST 2000

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Hi again,

I have implemented a Python C/API module `lazy' that you can use to put a
Python dictionary to a "lazy" mode.
You can find the lazy module in

http://cens.ioc.ee/~pearu/misc/lazy-0.1.tar.gz

Here is a Python session showing lazy in action:

  >>> import lazy
  >>> d = {'a':4}
  >>> lazy.set(d,lambda k:3)              # set d to lazy mode
  >>> print d
  {'_lazy_cb': <function <lambda> at 0x8112e24>, 'a': 4}
  >>> d['b']
  3
  >>> print d
  {'_lazy_cb': <function <lambda> at 0x8112e24>, 'b': 3, 'a': 4}
  >>> del d['_lazy_cb']                   # disable lazy mode
  >>> d['c']
  Traceback (most recent call last):
    File "<stdin>", line 1, in ?
    KeyError: c

And another example:

>>> import lazy
>>> def fun(k):
...     print 'Creating variable %s'%(`k`)
...     return k
... 
>>> lazy.set(locals(),fun)
>>> print a+b+c
Creating variable 'a'
Creating variable 'b'
Creating variable 'c'
abc
>>> print lazy.set.__doc__
lazy.set(dict,func) - set dictionary dict to a "lazy" mode with
a callback function func.

"lazy" mode means that the following statement
    dict[<name>] = func(<name>)
is executed whenever dict has no key <name>.

WARNING: if dict is set to "lazy" mode, dict.has_key(<name>)
returns always 1 and dict[<name>] is set to func(<name>).

To disable the "lazy" mode for dict, do
    del dict['_lazy_cb']


Be lazy and have fun!-)

Pearu

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