On Tue, Feb 19, 2013 at 3:51 PM, Miki Tebeka wrote:

Why not:

...

parser.add_argument('--spam', default=os.environ.get('SPAM', 7))

Mainly because then you can't swap in different dictionaries to resolve SPAM (when specifying "env" to ArgumentParser).

Can you elaborate on this requirement?

The other reason is that it's making common code shorter, which is a win IMO.

How common is such code? YMMV here... I don't think it's nearly common enough to warrant adding complexity to a stdlib module in order to implement a non-orthogonal feature. In general, I'm -1 on the idea. argparse is for parsing command line arguments. Python provides you convenient access to env vars via os.environ. Why mix up the two? Eli

On 20 February 2013 06:59, Vito De Tullio wrote:

Eli Bendersky wrote:

...

In general, I'm -1 on the idea. argparse is for parsing command line arguments. Python provides you convenient access to env vars via os.environ. Why mix up the two?

well, command line arguments, environmental variables and, I add, configuration files are commonly intertwined.

While argparse focus on the first one, there are cases where you want some "layer" on top of it and on os.environ and on... ConfigParser?) to DRY.

configglue combines support for config files (and hierarchies of config files) with command line arguments. https://pypi.python.org/pypi/configglue/ Michael

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On Tuesday, February 19, 2013 8:29:48 PM UTC-8, Eli Bendersky wrote:

On Tue, Feb 19, 2013 at 3:51 PM, Miki Tebeka javascript:

...

wrote:

...

Why not:

...

parser.add_argument('--spam', default=os.environ.get('SPAM', 7))

Mainly because then you can't swap in different dictionaries to resolve SPAM (when specifying "env" to ArgumentParser).

Can you elaborate on this requirement?

Sure. The idea is the you have some kind of "parameter resolution" (very much like the interpreter is resolving variables). You first look into the command line, and if not found you query a dictionary. Most times, this dictionary will be os.environ. However you can pass your own dictionary to resolve the parameters (for testing, configuration files). You can even use something like Raymonds Nested Contextshttp://code.activestate.com/recipes/577434-nested-contexts-a-chain-of-mappin...for that matter.

On Thu, Feb 21, 2013 at 10:18 AM, Eli Bendersky wrote:

What about config files? Mix them into argparse too? Oh, and support for .ini/XML/YAML/JSON/sqlite configs, please!

Sarcasm aside (don't take it personally ;-), my point is this: argparse is a nice, orthogonal library for dealing with command-line arguments. Let's keep it this way. Python gives you tools to *very easily* mix up different configuration paths, with really minimal effort.

Indeed - a layered architecture is the way to go here. argparse can be a *component* of a comprehensive configuration system, but it shouldn't try to *become* a comprehensive configuration system. Cheers, Nick. -- Nick Coghlan | ncoghlan@gmail.com | Brisbane, Australia

What about config files? Mix them into argparse too? Oh, and support for .ini/XML/YAML/JSON/sqlite configs, please!

Well, baby steps toward configuration solution :) The other thing is that unlike config files which have many formats, environment has one uniform access to it.

On Tue, Feb 19, 2013 at 3:51 PM, Miki Tebeka wrote:

...

Why not:

parser.add_argument('--spam', default=os.environ.get('SPAM', 7))

Mainly because then you can't swap in different dictionaries to resolve SPAM (when specifying "env" to ArgumentParser).

Couldn't you achieve this with a simple helper function? Something along the lines of-- env = {'SPAM': 9} parser = argparse.ArgumentParser() def add_argument(key, *args, **kwargs): if key in env: kwargs['default'] = env[key] parser.add_argument(*args, **kwargs) add_argument('SPAM', '--spam', default=7) ... This also allows env to be an arbitrary dictionary. --Chris