config2py 0.1.36

Simplified reading and writing configurations from various sources and formats

config2py

Simplified reading and writing configurations from various sources and formats.

To install: pip install config2py

Documentation

The cherry on top: config_getter

from config2py import config_getter

Let's start with an extremely convenient, no questions asked, object. Later, we'll look under the hood to show the many tools that support it, and can be shaped to fit many desired behaviors.

What config2py.config_getter(key) will do is:

• search for key in your environment variables, and if not found...
• ... search for it in a default local directory (more on that later), and if not found...
• ... ask the user to enter the value that key should have, and then put it in the local directory mentioned above.

Note: The "... ask the user to enter the value..." will be activated only when in an interactive environment (python console, jupyter notebook, etc.), as decided by the config2py.is_repl() function

config_getter('HOME')  # if you are using Linux/MacOS
# config_getter('USERPROFILE')  # if you are using Windows

'/Users/thorwhalen'

Now, normally all systems come with a HOME environment variable (or a USERPROFILE on windows), so the above should always work fine. But see what happens if you ask for a key that is not an environment variable:

my_config_val = config_getter('_TEST_NON_EXISTING_KEY_')  # triggers a user input dialog
# ... I enter 'my config value' in the dialog, and then...

my_config_val

'my config value'

But if I do that again (even on a different day, somewhere else (on my same computer), in a different session), it will get me the value I entered in the user input dialog.

my_config_val = config_getter('_TEST_NON_EXISTING_KEY_')  # does not trigger input dialog
my_config_val

'my config value'

And of course, we give you a means to delete that value, since config_getter has a local_configs mapping (think dict) to the local files where it has been stored. You can do all the usual stuff you do with a dict (except the effects will be on local files), like list the keys (with list(.)), get values for a key (with .[key]), ask for the number of keys (len(.)), and, well, delete stuff:

if '_TEST_NON_EXISTING_KEY_' in config_getter.configs:
    del config_getter.configs['_TEST_NON_EXISTING_KEY_']

This tool allows you to:

• not have to set up any special configs stuff (unless you want/need to)
• enables you to share your notebooks (CLIs etc.) with others without having to polute the code with configs-setup gunk...
• ... including when you put local file/folder paths (or worse, secrets) in your notebook or code, which others then have to edit (instead, here, just enter a probably-unique name for the needed resource, then enter your filepath in the user input dialog instead)

This is very convenient situation where user input (via things like __builtins__.input or getpass.getpass etc) is available. But you should not use this to manage configurations/resources anywhere were there's not a user to see and respond to the builtin user input dialog

Don't fret though, this config_getter is just our no-BS entry point to much more. Let's have a slight look under its hood to see what else we can do with it.

And of course, if you're that type, you can already have a look at the documentation

simple_config_getter: Controlling your config_getter a bit more

If you look up for the definition of the config_getter function you imported above, you'll find this: config_getter = simple_config_getter(). That is, it was created by simple_config_getter with its default arguments. Let's have a look at what these are.

In fact, simple_config_getter is a function to make configuration getters that ressemble the one we've seen above:

But where you can control what the central store (by default "Local App Data Files" store) is, and whether to first search in environment variables or not, and whether to ask the user for the value, if not found before, or not.

from config2py import simple_config_getter, get_configs_local_store
from i2 import Sig

print(*str(Sig(simple_config_getter)).split(','), sep='\n')

(configs_src: str = '.../.config/config2py/configs'
*
first_look_in_env_vars: bool = True
ask_user_if_key_not_found: bool = None
config_store_factory: Callable = <function get_configs_local_store at 0x10a457370>)

first_look_in_env_vars specifies whether to look into environment variables first, or not.

ask_user_if_key_not_found specifies whether to ask the user if a configuration key is not found. The default is None, which will result in checking if you're running in an interactive environment or not. When you use config2py in production though, you should definitely specify ask_user_if_key_not_found=False to make that choice explicit.

The configs_src default is automatically set to be the config2py/configs folder of your systems's "App Data" folder (also configurable via a CONFIG2PY_APP_DATA_FOLDER environment variable).

Your central store will be config_store_factory(configs_src), and since you can also specify config_store_factory, you have total control over the store.

The default config_store_factory is get_configs_local_store which will give you a locally persisted store where if configs_src:

• is a directory, it's assumed to be a folder of text files.
• is a file, it's assumed to be an ini or cfg file.
• is a string, it's assumed to be an app name, from which to create a config folder for with the default method

Setting the config key search path

If you check out the code for simple_config_getter, you'll find that all it it is simply setting the sources argument for the get_config function. Something more or less like:

configs = config_store_factory(configs_src)
source = [
    os.environ,  # search in environment variables first
    configs,  # then search in configs
    user_gettable(configs)  # if not found, ask the user and store in 
]
config_getter = get_config(sources=source)

So you see that you can easily define your own sources for configs, and in what order they should be searched. If you don't want that "ask the user for the value" thing, you can just remove the user_gettable(local_configs) part. If you wanted instead to add a place to look before the environment variables -- say, you want to look in to local variables of the scope the config getter is defined (not called), you can stick locals() in front of the os.environ.

So you see that you can easily define your own sources for configs, and in what order they should be searched. If you don't want that "ask the user for the value" thing, you can just remove the user_gettable(local_configs) part. If you wanted instead to add a place to look before the environment variables -- say, you want to look in to local variables of the scope the config getter is defined (not called), you can stick locals() in front of the os.environ.

Let's work through a custom-made config_getter.

from config2py import get_config, user_gettable
from dol import TextFiles
import os

my_configs = TextFiles('~/.my_configs/')  # Note, to run this, you'd need to have such a directory!
# (But you can also use my_configs = dict() if you want.)
config_getter = get_config(sources=[locals(), os.environ, my_configs, user_gettable(my_configs)])

Now let's see what happens when we do:

config_getter('SOME_CONFIG_KEY')

Well, it will first look in locals(), which is a dictionary containing local variables where the config_getter was defined (careful -- not called!!). This is desirable sometimes when you define your config_getter in a module that has other python variables you'd like to use.

Assuming it doesn't find such a key in locals() it goes on to try to find it in os.environ, which is a dict containing system environment variables.

Assuming it doesn't find it there either (that is, doesn't find a file with that name in the directory ~/.my_configs/), it will prompt the user to enter the value of that key. The function finally returns with the value that the user entered.

But there's more!

Now look at what's in my_configs! If you've used TextFiles, look in the folder to see that there's a new file. Either way, if you do:

my_configs['SOME_CONFIG_KEY']

You'll now see the value the user entered.

This means what? This means that the next time you try to get the config:

config_getter('SOME_CONFIG_KEY')

It will return the value that the user entered last time, without prompting the user again.

A few notable tools you can import from config2py

• get_config: Get a config value from a list of sources. See more below.
• user_gettable: Create a GettableContainer that asks the user for a value, optionally saving it.
• ask_user_for_input: Ask the user for input, optionally masking, validating and transforming the input.
• get_app_data_folder: Returns the full path of a directory suitable for storing application-specific data for a given app name.
• get_configs_local_store: Get a local store (mapping interface of local files) of configs for a given app or package name
• configs: A default store instance for configs, defaulting to a local store under a default configuration local directory.

get_config

Get a config value from a list of sources.

This function acts as a mini-framework to construct config accessors including defining multiple sources of where to find these configs,

A source can be a function or a GettableContainer. (A GettableContainer is anything that can be indexed with brackets: obj[k], like dict, list, str, etc..).

Let's take two sources: a dict and a Callable.

>>> def func(k):
...     if k == 'foo':
...         return 'quux'
...     elif k == 'green':
...         return 'eggs'
...     else:
...         raise RuntimeError(f"I don't handle that: {k}")
>>> dict_ = {'foo': 'bar', 'baz': 'qux'}
>>> sources = [func, dict_]

See that get_config go through the sources in the order they were listed, and returns the first value it finds (or manages to compute) for the key:

get_config finds 'foo' in the very first source (func):

>>> get_config('foo', sources)
'quux'

But baz makes func raise an error, so it goes to the next source: dict_. There, it finds 'baz' and returns its value:

>>> get_config('baz', sources)
'qux'

On the other hand, no one manages to find a config value for 'no_a_key', so get_config raises an error:

>>> get_config('no_a_key', sources)
Traceback (most recent call last):
...
config2py.errors.ConfigNotFound: Could not find config for key: no_a_key

But if you provide a default value, it will return that instead:

>>> get_config('no_a_key', sources, default='default')
'default'

You can also provide a function that will be called on the value before it is returned. This is useful if you want to do some post-processing on the value, or if you want to make sure that the value is of a certain type:

This "search the next source if the previous one fails" behavior may not be what you want in some situations, since you'd be hiding some errors that you might want to be aware of. This is why allow you to specify what exceptions should actually be considered as "config not found" exceptions, through the config_not_found_exceptions argument, which defaults to Exception.

Further, your sources may return a value, but not one that you consider valid: For example, a sentinel like None. In this case you may want the search to continue. This is what the val_is_valid argument is for. It is a function that takes a value and returns a boolean. If it returns False, the search will continue. If it returns True, the search will stop and the value will be returned.

Finally, we have egress : Callable[[KT, TT], VT]. This is a function that takes a key and a value, and returns a value. It is called after the value has been found, and its return value is the one that is returned by get_config. This is useful if you want to do some post-processing on the value, or before you return the value, or if you want to do some caching.

>>> config_store = dict()
>>> def store_before_returning(k, v):
...    config_store[k] = v
...    return v
>>> get_config('foo', sources, egress=store_before_returning)
'quux'
>>> config_store
{'foo': 'quux'}

Note that a source can be a callable or a ``GettableContainer`` (most of the
time, a ``Mapping`` (e.g. ``dict``)).
Here, you should be compelled to use the resources of ``dol``
(https://pypi.org/project/dol/) which will allow you to make ``Mapping``s for all
sorts of data sources.

For more info, see: https://github.com/i2mint/config2py/issues/4

user_gettable

So, what's that user_gettable?

It's a way for you to specify that the system should ask the user for a key, and optionally save it somewhere, plus many other parameters (like what to ask the user, etc.)

from config2py.base import user_gettable

s = user_gettable()
s['SOME_KEY'] 
# will trigger a prompt for the user to enter the value of SOME_KEY
# ... and when they do (say they entered 'SOME_VAL') it will return that value

# And if you specify a save_to store (usually a persistent MutableMapping made with the dol package)
# then it will save the value to that store for future use
d = dict(some='store')
s = user_gettable(save_to=d)
s['SOME_KEY'] 

More on that another day...