Another option would be to refactor your function so that it is a generator expression using the yield keyword.
On Sun, Jun 17, 2012 at 7:40 PM, Peter Otten <__pete...@web.de> wrote: > Gelonida N wrote: > > > I'm having a module, which should lazily evaluate one of it's variables. > > Meaning that it is evaluated only if anybody tries to use this variable. > > > > At the moment I don't know how to do this and do therefore following: > > > > > > ####### mymodule.py ####### > > var = None > > > > def get_var(): > > global var > > if var is not None: > > return var > > var = something_time_consuming() > > > > > > > > Now the importing code would look like > > > > import mymodule > > def f(): > > var = mymodule.get_var() > > > > The disadvantage is, that I had to change existing code directly > > accessing the variable. > > > > > > I wondered if there were any way to change mymodule.py such, that the > > importing code could just access a variable and the lazy evaluation > > would happen transparently. > > > > import mymodule > > def f(): > > var = mymodule.var > > > > > > > > Thanks in advance for you suggestions > > You can inject arbitrary objects into sys.modules: > > >>> import sys > >>> class MyModule(object): > ... def __init__(self): > ... self._var = None > ... @property > ... def var(self): > ... result = self._var > ... if result is None: > ... print "calculating..." > ... self._var = result = 42 > ... return result > ... > >>> sys.modules["mymodule"] = MyModule() > >>> import mymodule > >>> mymodule.var > calculating... > 42 > >>> mymodule.var > 42 > > > -- > http://mail.python.org/mailman/listinfo/python-list >
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