You can't change a Python function's local variables from outside
In an aside in a recent entry, I wrote:
With sufficient cleverness, you can construct a version of
capture()that is passed
store's name and puts the result in it directly, without needing you to make it an array and use
I'm wrong. In Python, no outside power can change a function's local
variables (more precisely, no outside power can change the name
bindings, doing the equivalent of '
something'). While you can make a version of
capture() that sets
global variables, setting a local variable in the function that called
it is beyond its power.
Once I thought about it, this limitation is a logical consequence of how Python implements local variables. Since local variables aren't stored in a Python data structure, the CPython core would have to implement special functions to modify their values, which would only be useful for debuggers and people who want to commit dubious hacks.
(This does mean that not even Python debuggers can change local variables, although not all of them will clearly tell you this.)