Johan Grönqvist schrieb:
Hi All,
I find several places in my code where I would like to have a variable
scope that is smaller than the enclosing function/class/module definition.
One representative example would look like:
----------
spam = { ... }
eggs = { ... }
ham = (a[eggs], b[spam])
----------
The essence is that for readability, I want spam and eggs in separate
definitions, but for clarity, I would like to express the fact that they
are "local to the definition of ham", i.e., they are not used outside of
the definition of ham.
The language reference at
<http://docs.python.org/reference/executionmodel.html> says that "The
following are blocks: a module, a function body, and a class
definition." (all other cases seem to refer to dynamic execution using
eval() or similar). Python 3 and 2.6 seem to have identical scope rules.
In the other languages I have used I can either use braces (C and
descendants) or use let-bindings (SML, Haskell etc.) to form local scopes.
Are there suggestions or conventions to maximize readability for these
cases in python? (Execution time is not important in the cases I
currently consider.)
Regards
Johan
I think it is not possible to realize something like braces in C or
let-bindings in python. But here are some Ideas to work around this problem:
1) If you define all this in the global namespace you could remove your
temporary variables afterwards, e.g.
spam = 1
ham = (spam,)
del globals()['spam']
This only works for the global namespace and not for the local! I
wouldn't recommend it.
2) create a method, which initializes ham
def make_ham():
spam = {...}
egg = {...}
return (egg, spam)
ham = make_ham()
This makes it easier to reuse ham in other situations and wouldn't
expose spam or egg.
3) Make a class for your ham data structure
If ham is so complex that you have to split it up, it may makes sense to
create a class for it. Of course this would need refactoring of the
code, but it's more readable and extensible than packing your data in
tuples, lists or dictionaries.
- Patrick
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