Add to locals() in Python 3.2+?

Question

I'm trying to programmatically define several variables in the local namespace:

for build_step in 'prepare', 'configure', 'make', 'stage', 'package', 'all':
    p = build_subparsers.add_parser(build_step)
    p.set_defaults(build_step=build_step)
    if build_step != 'package':
        p.add_argument('specfile')
    locals()['build_'+build_step+'_parser'] = p
build_prepare_parser

NameError: global name 'build_prepare_parser' is not defined

However after running this code, none of the variables I presumed to create actually exist despite appearing in locals(). How do I do this in Python 3.2?

Update0

I know locals() is a bad idea, that's why I'm asking this question.

"Note: The contents of this dictionary should not be modified; changes may not affect the values of local and free variables used by the interpreter." — Ignacio Vazquez-Abrams
– Ignacio Vazquez-Abrams, Commented Jun 16, 2011 at 0:18
This is a really bad way of doing this, Why are you editing locals like this, why so many variables. Use a list. — Jakob Bowyer
– Jakob Bowyer, Commented Jun 16, 2011 at 0:20

senderle · Accepted Answer · 2011-06-16 00:22:21Z

6

The answer is: don't do that.

If you want to programmatically store values, use a container:

>>> d = dict()
>>> d['a'] = 5

Or create a container class, if you really must.

>>> class Container(object):
...     pass
... 
>>> c = Container()
>>> setattr(c, 'a', 5)
>>> c.a
5

answered Jun 16, 2011 at 0:22

senderle

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1 Comment

senderle Over a year ago

See here for a slightly more sophisticated container class.

John La Rooy · Accepted Answer · 2011-06-16 00:45:29Z

5

Why not give build it's own namespace?

class Build(dict):
    def __init__(self):
        self.__dict__ = self

build = Build()
for build_step in 'prepare', 'configure', 'make', 'stage', 'package', 'all':
    p = build_subparsers.add_parser(build_step)
    p.set_defaults(build_step=build_step)
    if build_step != 'package':
        p.add_argument('specfile')
    build[build_step+'_parser'] = p
build.prepare_parser

answered Jun 16, 2011 at 0:45

John La Rooy

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2 Comments

senderle Over a year ago

I like this one... but somehow the self.__dict__ = self thing makes me feel funny inside. What if you did this?

John La Rooy Over a year ago

@senderle, sure, that would work. You could also add nice __repr__ etc to the class

Russell Borogove · Accepted Answer · 2011-06-16 00:21:15Z

0

According to the docs for locals():

The contents of this dictionary should not be modified; changes may not affect the values of local and free variables used by the interpreter.

Try putting them in globals() (which is the symbol dictionary for the current module, not truly global.)

answered Jun 16, 2011 at 0:21

Russell Borogove

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