On 3/5/07, Guido van Rossum <[EMAIL PROTECTED]> wrote:
> I don't know too many good use cases for
> locals() apart from "learning about the implementation" I think this
> might be okay.
Since I'm watching this list for any discussion on the traceback
threads, I figured I would point out the most common use I know
for locals() is in string interpolation when there are many local
variables, eg:
a = "spam"
b = "egg"
...
y = "foo"
z = "bar"
print fmtstr % locals()
The next most is to deal with a large number of input parameters, as
this from decimal.py:
def __init__(self, prec=None, rounding=None,
traps=None, flags=None,
_rounding_decision=None,
Emin=None, Emax=None,
capitals=None, _clamp=0,
_ignored_flags=None):
...
for name, val in locals().items():
if val is None:
setattr(self, name, _copy.copy(getattr(DefaultContext, name)))
else:
setattr(self, name, val)
and this example based on a post of Alex Martelli's:
def __init__(self, fee, fie, foo, fum):
self.__dict__.update(locals())
del self.self
In both cases they are shortcuts to "reduce boilerplate".
I've more often used the first form in my code. If an
inner local returned a superset of the items it returns now,
I would not be concerned.
I've rarely used the 2nd form in my code. The only way
I can see there being a problem is if a function defines
a class, which then uses the locals() trick, because
>>> def blah():
... a = 6; b = 7
... class XYZ(object):
... def __init__(self):
... c = a
... print "in the class", locals()
... print "in the function", locals()
... XYZ()
...
>>> blah()
in the function {'a': 6, 'XYZ': <class '__main__.XYZ'>, 'b': 7}
in the class {'a': 6, 'c': 6, 'self': <__main__.XYZ object at 0x72ad0>}
the code in the class's initializer will have more locals. I've
never seen code like this (class defined in a function, with __init__
using locals()) and it's not something someone would write
thinking it was a standard way of doing things.
In both cases I'm not that bothered if it's implementation specific.
Using locals has the feel of being too much like a trick to get
around having to type so much. That's what editor macros are for :)
Andrew
[EMAIL PROTECTED]
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