[Tutor] What Eval() Hath Men Wrought
alan.gauld at blueyonder.co.uk
Thu Jun 24 12:17:11 EDT 2004
> The C way to do it is to pass in a pointer to a function.
And you can pass a function object in Python too but...
> This is good because C nicely checks that the function
> 1) is actually a function
> 2) takes the right arguments
> 3) returns the right type.
Python does none of these, although you can explicitly
check the object is callable in the receiving code.
> The Matlab way to do it is to pass a string that contains
> the function name, and to use the Matlab feval function,
> .... but instead can use the form feval('function_name',argument).
You can use the Python apply() function to do a similar thing,
it takes a callable object and a tuple of arguments to be passed
to the callable.
> you get weird errors if the function name is wrong, or if
> the function takes an unexpected kind of argument or returns
> an unexpected type.
Yes, thats always a problem with this type of eval() behaviour.
> What is the right way to do this in Python?
There is no right way, mostly I would pass a function reference
as my preferred route and apply() as a close second if, for
example the functions took different numbers of arguments.
Note that you can get the callable function object from its
name by using the local namespace dictionary.
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