== Initializing Python struct objects with optional defaults

Recently I was writing code to register names and their
attributes. There were enough attributes that I didn't want to specify
all of them all of the time, so I did the obvious Python thing: I made
the _register()_ function take a bunch of keyword arguments that had
default values. The attributes are stored with a
[[_struct_ object|EmulatingStructsInPython]], because I wanted an
_attrs.attribute_ syntax for accessing them.

The straightforward way to initialize the struct object was to write
'_vi = ViewInfo(factory = factory, onDir = onDir, ...)_', but that
sort of repetition is annoying, especially when I had a perfectly good
set of name/value pairs in the form of _register()_'s arguments. If
only I could get at them.

It turns out that you can use the _locals()_ dictionary for this, *if*
you use it before you set any local variables in the function. So:

>  class ViewInfo(Struct):
>    pass
>  
>  def register(name, factory, onDir = False, \
>               onFile = True, ...):
>    vi = ViewInfo(**locals())
>    view_dict[name] = vi

(I did not strictly need the _name_ attribute in the ViewInfo data,
but it doesn't do any harm and it meant I could use _locals()_
straight.)

A similar pattern can be done directly in a _struct_ class as:

>  class ViewInfo:
>    def __init__(self, name, factory, \
>                 onDir = False, ...):
>      for k, v in locals().items():
>        if k != "self":
>          setattr(self, k, v)

(You really want to exclude _self_, since circular references make the
garbage collector work harder than necessary.)