Johan Grönqvist wrote:
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.
delete spam, eggs
rather effectively says that the reader can also forget the bindings.
Execution time is minimal since no object is gc'ed.
This works with function locals also:
>>> def f():
i=1; del i; print (i)
>>> f()
Traceback (most recent call last):
File "<pyshell#6>", line 1, in <module>
f()
File "<pyshell#5>", line 2, in f
i=1; del i; print (i)
UnboundLocalError: local variable 'i' referenced before assignment
However, since probably a majority of non-function bindings are rather
local, I do not see that this really improved readability.
Within a module intended to be imported, using _spam, _eggs would signal
that they are only inted for local use. Delete if you want to enforce that.
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.
Not exactly. In 3.0, comprehensions define a new scope by virtue of
being implicit function bodies.
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.
I consider that simplicity of Python scoping to be a major feature; it
is one of the reasons I use it.
tjr
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