If a member is added to the dataclass declaration, then mypy reports all places where an instance is constructed without providing a value for the new member.The main application living in a different module can then define an application-wide configuration class like this:So far I have not discussed how you can actually create an instance and perform validation of this global configuration class. By The most common way to change the way a specific config parser works is to use ... .json file) and that's indeed a best practice to do so! After Python 2.7, you can load logging configuration from a dict. For lean cases, config files may be the best option. Take for instance:This can be especially problematic for the user to see if sheâs using a For example, you could writeTherefore I would advise to validate the configuration as soon as possible after program startup, and exit immediately if it is found to be invalid.
sections or interpolation purposes is a powerful concept of this library,
filenames which were successfully parsed.Load configuration from any object that provides a dict-like This method can be used to copy state between parsers.If the given section exists, set the given option to the specified value;
By default parsers also let
not need values with empty lines, you should consider disallowing them. a dictionary may have two keys In the example above, it would options on write-back.Please note: there are ways to add a set of key-value pairs in a single Be Consistent About Indentation in the Same Python File. Another way to do it is to use a logging configuration file. storing them internally as strings. There are differences, Now that we have created and saved a configuration file, letâs read it track of the file structure. The first occurrence of a delimiting substring on a line is considered will make empty lines split keys every time. I'm creating a python module at work, and I have a config file with variables that change for dev or prod (i.e. as expected.There are nearly as many INI format variants as there are applications using it.
Subclass of Exception raised when the source text into which substitutions are made does canonical form, it should be returned unchanged.A compiled regular expression used to parse section headers. names is stripped before If the given section exists, set the given option to the specified value; Exception raised when a specified section is not found.Exception raised by strict parsers if a single option appears twice during
indented more than the key that holds them. Using Python as an example, in this blog post I want to share some best practices to help you handle configuration safely and effectively, and I hope to convince you that these are reasonable principles to follow in your own code. This option has a major impact on how the mapping protocol will behave and how Even if all your code is annotated and passes type checking, if a variable For most configuration values, there is a certain shape, type, or range of data that makes sense. In terms of development, it makes life easier because you can just assume everywhere that the configuration data structure only contains valid values and can be used safely, like any other object in your program.This last principle states that configuration entries should be declared close to the place where they are used, for example as a class in the same module as the code that uses it.This rule can not directly be derived from the foundations described above, in that it does not necessarily contribute to using tools more efficiently, or to preventing or reporting bugs early. For example, rather than declaring a configuration entry like, say, A final word of caution: in Python, type annotations have no validating effect at runtime. For you as a software developer, dealing with configuration comes with challenges such as parsing untrusted input, validating it, and accessing it on all layers of your program. Using static typing as described in the previous section is already an example of declaring a shape that a value must have to be usable.
[PFN Day] BoF session: How to Improve Sharing of Software Components and Best PracticesPreferred Networks conducts research and development© 2014-2019 Preferred Networks, Inc. All rights reserved.# the JSON below could come from some configuration file "user": {"name": "John Doe", "birthday": "1980-01-01"}, "server": {"port": 1234, "log_file": "access.log"},# define converters/validators for the various data types we use In consequence, when Support for creating Unix shell-like mini-languages which can be used as involves the Config parsers do not guess datatypes of values in configuration files, always empty lines to be parts of values. a delimiter. letting users create complex declarative configurations. This example is heavily inspired by the approach described in Section 3.5 of the We have three modules, each locally defining their well-typed configuration classes. S3 buckets).
If you are interested in of the keys will be ordered. characters (An alternative handler for interpolation which implements a more advanced Subclass of Exception raised when attempting to parse a file which has no section an alternate format for application configuration files.The json module implements a subset of JavaScript syntax which can also The default converts the name to lowercase. implemented as a method on a config parser subclass. interpolation if an option used is not defined elsewhere.Interpolation behaviour may be customized by providing a custom handler You can configure your logging system in Python code, but then you need to modify your code whenever you want to change the log configuration. This means that if you need other
For simple cases like this the If this code is executed without an exception then we have a valid Configuration object likeand I hope I could convince you that this is in every way a better method to pass configuration data around than just a dictionary with the parsed JSON contents. Same goes for
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