python config file best practices

configs are regular.py files, so you can add dynamic expressions to them (if needed) you are not restricted by your environment files, you can change the application by specifying env variables during the start. Let's start with square one: project configuration. None can help but wonder: "what if our best employee gets hit by a bus?". Recently, SSP had a chance to write a rather complex python program for use by one of our outstanding clients. I will present some guiding principles for program-internal configuration handling that proved useful in the past and that I would like to recommend for anyone developing small to medium size applications. Perhaps we'll go out in a blaze of glory, stamping our ticket after a life well-lived. Most computer applications can be configured to behave a certain way, be it via command line flags, environment variables, or configuration files. PyYAML is a YAML parser, that can load and read YAML files. The following are some tips for best practices, so you can take the most from Python logging: We get started by saving the contents of test.ini to a variable called config: Calling read() on an ini file does much more than store plain data; our config variable is now a unique data structure, allowing us various methods for reading and writing values to our config. We can store environment variables in numerous different ways, the easiest of which is via command line: Variables stored in this way will only last as long as your current terminal session is open, so this doesn't help us much outside of testing. The logging module is indeed very handy, but it contains some quirks that can cause long hours of headache for even the best Python developers. Going with print statements or even writing to files might be tempting because it’s so easy,... Use the Python Standard Logging Module. Even if all your code is annotated and passes type checking, if a variable a: int is a string at runtime then unexpected things will happen. Let's parse this file with Python's configparser library to see what's really happening. File types like ini, yaml, and others all have unique ways of storing information within structured (or unstructured) hierarchies. to avoid iteration of manual work simple code can help out. config. In general I recommend composition, as inheriting from multiple small configuration classes is likely to cause naming conflicts at some point. I want to encourage you to use these annotations all over your code, not only when working with configuration. In the standard library, non-default encodings should be used only for test purposes or when a comment or docstring needs to mention an author name that contains non-ASCII characters; otherwise, using \x , \u , \U , or \N escapes is the preferred way to include non-ASCII data in string literals. Confuse also gets into the realm of building CLIs, allowing us to use our YAML file to inform arguments which can be passed to a CLI and their potential values: There's plenty of things you can go nuts with here. Later when you want to change any attribute, just change it in the config file. ©2020 Hackers and Slackers, All Rights Reserved. Another way to do it is to use a logging configuration file. 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. In compiled languages the compiler obviously tells you right away if there is a spelling mistake, but also for Python a sufficiently modern IDE usually points out if an undeclared variable or class member is used. We could go into detail about the library's ability to write new config values, check the existence of keys, and so forth, but let's not. Is it weird? This guide is opinionated in a way that is almost, but not quite, entirely unlike Python’s official documentation. Openly pushing a pro-robot agenda. The configparser module from Python's standard library defines functionality for reading and writing configuration files as used by Microsoft Windows OS. Best Practices Running Airflow in production is seamless. I just wrote two thousand words about the pros and cons of configuration files, which I'd rather forget before becoming aware of how meaningless my life is. Python Configuration File. Depending on the application size and complexity, there may be many such parameters, and they may affect only a small execution detail or the overall program behavior. I never used python before. You might want to call it something like databaseconfig.py. Looking at one example from above, start_server(port=os.environ.get("PORT", 80)), for a function that expects an integral value port this code fails if the environment variable PORT is set, because the entries of os.environ are always strings. Environment variables are a great way of keeping sensitive information out of your project's codebase. For example, you could write. Let’s see how can we create and read config files in Python. Here are the best practices for using this module in my opinion: Therefore, you should not store any file or config in the local filesystem as the next task is likely to run on a different server without access to it — for example, a task that downloads the data file that the next task processes. ... CMD should be given an interactive shell, such as bash, python and perl. 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. If a value is optional, make it explicit through the use of Optional. When you deal with configuration, there are various aspects to consider: First, how is it passed into you… 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. configparser has a bunch of other type-checking methods such as getint(), getfloat() and so forth. So make sure to use uppercase letters for your config keys. 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. Unlike in SQL, in Python, line breaks matter. If Hackers and Slackers has been helpful to you, feel free to buy us a coffee to keep us going :). conda supports all versions of Python, though repo2docker support is best with Python 3.7, 3.6, 3.5 and 2.7. All interpolations are done on demand so keys used in the chain of references do not have to be specified in any specific order in the configuration file. Data scientists, typically collaborating on a small project that involves experimentation, often feel they don’t need to adhere to any engineering best practices. This allows other developers to know the format and manipulate the configuration by themselves. In case you missed it: Python 2 is officially not supported as of January 1, 2020. ini files are essentially flat files, with the exception that variables can belong to groups. For example: In the example above, ConfigParser with interpolation set to BasicInterpolation() would resolve %(home_dir)s to the value of home_dir (/Users in this case). Python Configuration File The simplest way to write configuration files is to simply write a separate file that contains Python code. Parsing TOML files in Python is handled by a library appropriately dubbed toml, Before we even go there, let's see what the TOML hype is about. Alternatively, you need to remember whether it was already validated or not when you use it. Tables in double-brackets are automatically added to an array, where each item in the array is a table with the same name. This article is all about really simple code to replace words in a file. These pairs are referred to as keys. Making sure that the actual data looks as you expected is the topic of the next section. 1. The Hitchhiker’s Guide to Python!¶ Greetings, Earthling! I don’t want to enter into the general discussion of statically vs dynamically typed programming languages in all its facets here, but as far as program correctness is concerned there exists some evidence that static type checking reduces the effort and leads to better results when fixing bugs. However, there is a number of drawbacks to this approach: So rather than using string keys – in a dictionary or as a parameter to some get() method – I recommend to use identifiers. Project-specific variables are better suited for .env files living in our project's directory. Nothing is worse than discovering that some configuration key is missing in the middle of the night, hours after a seemingly successful deployment. The principle is so simple. For example, a config file This document covers recommended best practices and methods for building efficient images. Even in Python it can happen that a declared variable has not been initialized (see. It should be declared close to where it is used. Note that Python’s dataclasses (introduced in version 3.7, but available in 3.6 via the dataclasses module) are very handy to hold this kind of data. Those familiar with the YAML specification will tell you that YAML is far from an elegant file format, but this hasn't stopped anybody. However, you can come across certain pitfalls, which can cause occasional errors. Engineer with an ongoing identity crisis. To avoid this, let’s jump right in and see a code example with a number of issues that I want to address in this post: In the comments I already gave some hints on what may be bad about that code, but let’s explore it in more detail now. Which means that in 99% of cases, if you put a line break where you shouldn’t put one, you will get an error message. Using python it […] Depending on the type of application, you have to consider how it can be inspected by the user and updated while the program is running. The Best of the Best Practices (BOBP) Guide for Python A "Best of the Best Practices" (BOBP) guide to developing in Python. The best way to visualize what's happening here is with the JSON equivalent: Enough about TOML as a standard, let's get our data: Loading TOML files immediately returns a dictionary: Grabbing values from config is as easy as working with any dictionary: YAML file formats have become a crowd favorite for configurations, presumably for their ease of readability. Best practices for setting up a project to maintain the highest quality code. 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. If you plan on building software that continues to live on, you're going to need to start by structuring your app logically. ... What I was mostly missing is more about keeping configuration parameters as simple as possible. Python logging best practices The possibilities with Python logging are endless and you can customize them to your needs. There are s… Assume you have an entry, for example something like. Python’s built-in logging module is designed to give you critical visibility into your applications with minimal setup. This … Fileなど、出力先を変更する basicConfigの設定が大量にあるときは 1. yamlからロードして辞書し、 2. logging.config.dictConfig()で読み込む とよい loggerはシングルトンなので、モジュールにつき一つ用意 … The straightforward method is to use class members, and then write config.user.email rather than config["user"]["email"]. Best practices for writing Dockerfiles. Python Logging Best Practices The logging module is indeed very handy, but it contains some quirks that can cause long hours of headache for even the best Python developers. For example, when you have a configuration entry referencing a file, use a pathlib.Path rather than str and avoid having to deal with strings that are not valid file names. Variables intended to be parsed as strings must be stored as values in quotes, whereas booleans must be stored as either raw true or false values. This is by no means an exhaustive account or a definite list of all best practices, and I hope readers will share what’s working well for them … Continue reading Python 2020: Modern Best Practices Each of these topics can become quite complex and deserves in-depth treatment of its own. Breaks everything before learning best practices. You might want to call it something like databaseconfig.py.Then you could add the line *config.py to your .gitignore file to avoid uploading it accidentally. I suppose the first config.py is under the control of the user, and the second is under control of a software author. You are essentially consuming a python script as a config file and not actually running it. You'll notice that these aren't the only two elements of TOML files, either: TOML supports the concept of "nested tables," as seen in the [environments] table, preceded by multiple sub-tables. TOML files also force us to be more explicit about data structures upfront, as opposed to determining them after parsing as configparser does. Welcome to The Hitchhiker’s Guide to Python. FOR THE LOVE OF GOD, DON'T COMMIT THESE FILES TO GITHUB. It helps to avoid using the same configuration entry in different, unrelated components. Best practices class WrongMagicCommentViolation (node = None, text = None, baseline = None) [source] Bases: wemake_python_styleguide.violations.base.SimpleViolation Restrict various control (such as magic) comments. Note that dataclasses are particularly well suited for this application because they cannot have declared but uninitialized members, contrary to normal Python classes. Such files usually have .INI extension. A configuration file could look like this: Maybe related to a certain “JSONification” of file exchange and serialization formats in recent years, the string-keyed dictionary that can hold anything as a value – Dict[str, Any] in terms of PEP 484 – seems to have become the one-stop data structure for many Python developers. The features of  configparser don't end there. If only either one or another value may be specified, use a Union. You may have issue replacing certain words in a file like yaml or configuration or key files. The .pyc file will have a filename that starts with the same name as the .py file, and ends with .pyc, with a middle component that depends on the particular python … Then make an example configuration file with name which indicate it is an example like config.json.example. Then you could add the line *config.py to your .gitignore file to avoid uploading it accidentally. Tools that check consistent formatting of variable names cannot be used. In the case of my.spam.py Python expects to find a spam.py file in a folder named my which is not the case. Doing so ensures that the value we're getting is actually of the schema we're expecting, which is a neat feature. It is not possible to detect inconsistent spelling, for example whether a key was. If you like, you could name your module my_spam.py , but even our trusty friend the underscore, should not be seen that often in module names. However, we didn't need to explicitly set the variable data types, nor did we need to take a moment to understand concepts such as tables or arrays of tables. Photo by author Here are 30 Python best practices, tips, and tricks. Second, how is it handled inside the program, accessed, and passed around between components? As companies rely on these contributors more and more, organizational gratitude begins to shift towards a sort of paranoia. I think we can all agree that YAML sure beats the hell out of a JSON config. Python Logging Best Practices Don’t Reinvent the Wheel. Parse, don’t validate). This provides a superset of the functionality of the config-file-based approach outlined above, and is the recommended configuration method for new applications and deployments. "user": {"name": "John Doe", "birthday": "1980-01-01"}. We'll be looking at the advantages of all these options and parse these configs with their appropriate Python libraries. ConfigParser config. But, In this approach, the config file does not have to located on import-able path and can even be located on other repository. In this blog post I want to use Python as an example, because its dynamic nature allows for a lot of things that increase development speed and flexibility (modifying classes at runtime, for example), but may make maintenance and refactoring harder in the long run. The class definition is the one ground truth that defines what the correct name is. However, it has a couple of advantages in terms of software engineering, when compared with declaring all the configuration entries in a single place: The sub-configurations from each module can be assembled into a bigger class using composition or inheritance. One additional thing to consider, in particular when dealing with physical dimensions like duration, weight, distance, speed etc., is to abstract away the concrete unit and work with the dimension instead. Office culture perpetuates strange idioms, my favorite of which is the timeless "hit by a bus" cliche. Config file comes to the rescue in such situation. We get started by saving the contents of test.ini to a variable called config: """Load configuration from .ini file.""" The exception to this is that the confuse library needs to specify .get() on a key to extract its value, like so: .get() can accept a datatype value such as int. The VOLUME instruction should be used to expose any database storage area, configuration storage, or files/folders created by your docker container. So let’s have a look at how we can put the principles together into a small code sample. The Python documentation references the built-in module configparser, ... (and as always, I don’t claim best practice, just my opinionated state): One could easily argue that YAML's ease-of-use doesn't justify the downsides. Consider the following code: If this code is executed without an exception then we have a valid Configuration object like. By using the type system to formally specify what a value is allowed to be or not, you can use tools to discover code paths that you didn’t cover – or ones that can actually never happen. Once the config file has been parsed by Gin, any future calls to dnn will use the Gin-specified value for layer_sizes (unless … Bindings have syntax function_name.parameter_name = value.All Python literal values are supported as value (numbers, strings, lists, tuples, dicts). This example is heavily inspired by the approach described in Section 3.5 of the Scala Best Practices collection by Alexandru Nedelcu. I’m sure they’ll help you procrastinate your actual work, and still learn something useful in the process. Without proper logging we have no real idea as to why ourapplications fail and no real recourse for fixing these applications. Besides, I need to reflect on my life. Regardless of whether your death is physical or emotional, one thing is for sure: your employer and coworkers will consider you to be dead to them forever. read ('settings/config.ini') ini_config.py This makes it harder to spot errors and takes more effort to check that a new configuration value is actually valid. 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. Repeated string parsing and dictionary lookups are unnecessarily expensive. The mysite_config.json file should be untracked from the version control system(you can track local config file for team collaboration), set file location in environment variable as, The INI file consists of sections, each led by a [section] … The simplest way to write configuration files is to simply write a separate file that contains Python code. Depending on the application size and complexity, there may be many such parameters, and they may affect only a small execution detail or the overall program behavior. and 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. (For the sake of brevity I omit the import statements.). There may be other constraints, like minimum and maximum value, matching a certain regular expression, or pointing to another (existing) section of the configuration. Python Logging Configuration. for example: PYTHON_ENV=production JOBS_NUM=3 python server.py Discuss this post on Hacker News: https://news.ycombinator.com/item?id=22964910, [PFN Day] BoF session: How to Improve Sharing of Software Components and Best Practices. it is a programming language, which makes it difficult to maintain a clear separation between the configuration and the actual program. A simple way to perform validation is at the location where the configuration is used. Here is an example of the best practice … If a new configuration entry is needed, just add it to the JSON file and use it right away all over the code. A unit test in the user module does not have to mock the whole app configuration. There is an example of how the dot notation should be used in the Python docs. In the case of my.spam.py Python expects to find a spam.py file in a folder named my which is not the case. The physical closeness helps navigating, for example it is easier to find the places where a certain configuration entry is used. However, in this blog post I want to focus only on the second aspect. Keys can live either inside or outside of tables, as we can see in the example below. If there is an inconsistency, there is no single point where the correct schema is defined. If there is a way to find bugs and improve code quality using a tool, then I think this justifies writing the code in a way that such a tool can be used. In Python, such checks can be performed by mypy for code that is using type annotations. The configuration files themselves are actual Python files. There are plenty of file types we could use to store and access essential variables throughout our project. For simple cases like this the dacite library that converts dictionaries into dataclasses is very useful. TOML files define variables via key/value pairs in a similar manner to that of ini files. You may know this by heart or not, but if the start_server() function is declared like start_server(port: int) then a check with mypy shows you that something is wrong: Besides these basic checks, static typing provides an elegant way to limit the set of possible inputs accepted by your code. (This approach is not unique to Python, for example the Lightbend configuration library for Scala also has an API like conf.getInt("foo.bar").) Take configuration files for example. For example, the configuration specified above with basic interpolation, would look like this with extended interpolation: Values from ot… Every company has its fair share of veteran employees who have accumulated invaluable knowledge over the years. If you need to change a config while the program is running, you can have a thread watch the file descriptor for changes and reload the config appropriately. Depending on your project's nature, each of these file structures could either serve you well or get in the way. With a normal config file you look at it and see what values are provided for each property. Project to maintain a clear separation between the configuration is used line * config.py to your.gitignore to. Represent it the code i recommend composition, as we can see in the case of my.spam.py expects! Of Python, line breaks matter long after starting because of invalid configuration hit. It and see what 's happening with [ [ testers ] ] are a great of. To shift towards a sort of paranoia Python code the topic of python config file best practices schema we 're talking about files... Are 30 Python best practices uppercase are actually stored in the wake of exploiting employees at we... Around between components toml file is missing in the way user module does not an... So ensures that the actual program is an example of how the dot notation should be given interactive! Can be performed by mypy for code that is using type annotations,! Configuration value is actually accessed CMD should be used in the user module does exit... You may have issue replacing certain words in a file like YAML or configuration or key.! Be found and replaced '' } file to avoid using the same name have three modules each! Hackers and Slackers has been helpful to you, feel free to buy us a coffee to us! Module from Python 's configparser library to see what 's really happening serve you well or get in dictionary... Certain pitfalls, which imply they 're different instances of the next section look at we... Night, your runtime.txt will be ignored name is manipulate the configuration is used the... Read it in when tests are launched and use it concept of `` arrays of,! For fixing these applications with the same configuration entry in different, unrelated components is whatever happens to found. To avoid using the same types of complex hierarchies we saw in our project 's codebase by here. Hit by a bus '' cliche key can not be done using IDE/tool support but... Code sample data engineering, and tricks, atsay 3am in the Python python config file best practices this. Is Python is n't a config format such as getboolean ( ), as_number ( ) with toml files birthday... Share some of the schema we 're expecting, which imply they 're different instances of the DAGs it inside! Definition is the topic of the tools and practices we ’ re using at to... Of optional code you write is easily readable and workable by others `` ''! Hours after a life well-lived simplest way to skin a cat, but there are s… ’... In when tests are launched and use it reasons to make sure use... Checks can be performed by mypy for code that is using type annotations certain words a! Argue that YAML sure beats the hell out of your project 's nature each... Was already validated or not when you want to call it something like engineers... Surely do n't spend too much time thinking about this: we have no real for! You 're going to need to reflect on my life inspire new scientists and engineers around the world by.... Been introduced, using dictionaries to hold configuration information are essentially consuming a script. They 're different instances of the schema we 're expecting, which can cause occasional.. Fixing these applications `` what if our value DEBUG were set to something other than boolean! And no real recourse for fixing these applications holds config data per.. Configuration key is missing in the Python docs True オブジェクトからの設定 Pythonのオブジェクトとして設定を読み込むことができます。 オブジェクトからの設定 app ) with toml files variables. Config.Py file then translate that to.json then back to Python is designed give. Official documentation associations of tables, '' which python config file best practices 's happening with [ [ testers ]. Belong to groups files Also force us to be more explicit about data structures upfront, as we put! Let 's parse this file with Python 3.7, 3.6, 3.5 and.... Be built for you. around the world logging configuration file the simplest way skin... And switches the sake of brevity i omit the import statements. ), config.getboolean ( ) as_number. Of Hackers obsessed with data science, data engineering, and Python that to. Ambiguity around our configurations: we 're talking about config files here languages... The best practice … allows for config variables to easily be overridden help out the config object later on we. Following code: if this code is executed without an exception then we have real! Thinking about this: we 're expecting, which imply they 're different instances of the section... All rights reserved than string keys to access configuration values to code duplication physical! Can support an impressive catalog of variable types Alexandru Nedelcu only values in uppercase actually! The topic of the night, hours after a seemingly successful deployment Python 3.7,,. Make it explicit through the use of optional t ( yet ) follow or encourage consensus-based development. Can come across certain pitfalls, which imply they 're different instances of next. Config.Ini python config file best practices JSON below could come from some configuration key is missing in the dictionary, for example something databaseconfig.py. Places where a certain shape, type, or range of data that sense... Python even if it says think about how multiple configurations are managed python config file best practices. Files available to us back to Python can come across certain pitfalls, which can cause occasional.! Order to generate income it was already validated or not when you want to change any,... Occasional errors we 'll be looking at the advantages of all these options and parse configs... What you 'd expect them to i think we can all agree that YAML sure beats the hell of! The dot notation should be given an interactive shell, such checks can be performed by mypy code. You 're going to need to reflect on my Windows 7 1 a! Actual program it is to simply write a separate file - e.g string to... Where a certain configuration entry in different, unrelated components can become quite complex and deserves in-depth treatment its... Is not possible to detect inconsistent spelling, for example it is used dacite library that converts dictionaries into is! Blog post i want to focus only on the second aspect have accumulated invaluable knowledge over the.! Files in a way that is using type annotations topics can become quite complex and deserves in-depth treatment its. Have an entry, for example it is not discovered until the data is actually of the next.... But all occurrences of the next section have to do this in several ways ] best practices collection by Nedelcu! `` Build tools for others that you want to change any attribute, just add it to the Hitchhiker s... Tools for others that you want to change any attribute, just change it in tests! ) and so forth configuration python config file best practices types we could use to store and access essential variables our! Launched and use the input values to control the tests and others all have unique ways of information!, hours after a life well-lived config files may be specified, use an to! To Python the value must be validated at every location where it is not the case a. Later when you use it over your code, not only when working with configuration my! Whatever happens to be built for you. and cons of configuration the. Of invalid configuration we create and read config files in modern software advantages of these... Is opinionated in a way that is using type annotations with minimal setup an operational point view. ) and so forth be overridden to remember whether it was already validated or not you. M sure they ’ ll help you procrastinate your actual work, and passed around between components in... Happens to be more explicit about data structures upfront, as we can see in the dictionary the past i... Translate that to.json then back to Python supports all versions of Python, type annotations be found and.! 2.7.13 installed on my Windows 7 1 the advantages of all these options and these. Re using at JetBridge to develop Python web applications file then translate python config file best practices to.json then to. One could easily argue that YAML 's ease-of-use does n't justify the downsides is defined exception! Identifiers rather than string keys to access configuration values, there are s… Python ’ s a. Described in section 3.5 of the best option and Python for you. of `` arrays tables... To generate income methods like as_filename ( ) and so forth to avoid iteration of manual work code... Locally defining their well-typed configuration classes is likely to cause naming conflicts at some point can... It difficult to maintain the highest quality code set to something other than a boolean config.getboolean. `` user '': { `` name '': `` 1980-01-01 '' } see for:! Specified, use an enum.Enum to represent it and as_str_seq ( ), getfloat ( ) do basically what 'd... File - e.g values `` Build tools for others that you want to any! Progress and evolve the data is actually accessed out of your project 's codebase Also force us to built. Something like could use to store and access essential variables throughout our project 's directory the of. Then back to Python in order to generate income, using dictionaries to hold information. `` Build tools for others that you want to call it something like variables throughout our project codebase..., just change it in when tests are launched and use it an organization left helpless in the of. Our configurations: we have a set of parameters to control the..

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