From Python to Dart - Day 2, Meet the dart CLI
The Dart language is unimaginable without the command-line utility (CLI) of the same name. This is a full-fledged tool that greatly simplifies the life of a developer in terms of its capabilities, far exceeding the built-in capabilities of the Python interpreter.
dart features available are project creation, source code analyzing and formatting, and even publishing packages to pub.dev and more.
Bear in mind that the goal of this cycle is not a complete immersion in Dart from scratch, but a quick acquaintance for those who already know how to develop, in particular, in the Python language.
Python does not have built-in capabilities for automated project creation, everything has to be done manually: create a folder structure, describe dependencies in
requirements.txt. Of course, there are third-party applications that make this process easier, such as poetry or Cookiecutter. However, they are third-party and require installation in a system or virtual environment. Dart has this feature built-in.
dart create is a CLI utility that can help you to create a project from the specified template.
$ dart create project_name
By default, this is a simple console application like dart-sass. However, this is not all. Using the
-t option, you can specify which template to use for creation, it can be:
||A simple console application (basic template).|
||Console application with tests.|
||A starting point for Dart libraries or apps.|
||Server based on shelf.|
||Web application with core libraries.|
dart create will first create the project structure and then try to load all required libraries from pub.dev. This behavior can be changed by specifying the
--no-pub flag when invoking the command.
Analogue from the world of Python:
poetry new project_name
Analyzing and formatting
When working with several people on one project, it is very often necessary to use a single style of code design, writing comments, using variable names, etc. In the Python world, we use linters [flake8] (https://flake8.pycqa.org/), various formatters (black, yapf, autopep8) and mypy for type checking. How can Dart help meet these challenges?
The utility allows you to perform static analysis of the source code and point out errors and shortcomings.
By default, the call will run a check and indicate errors and warnings, indicating the need to respond to the
info level with the
$ dart analyze [<DIRECTORY> | <DART_FILE>]
The behavior of the analyzer can be adjusted using the configuration file or comments in the code.
Using the command, we can style our source code according to the Dart guide.
$ dart format
This command will overwrite the files, formatting them "properly".
$ dart fix
Applies automatic fixes to source code files, fixing two types of errors:
- Analysis of issues related to automatic fixes (sometimes called quick-fixes or code actions))
- Issues related to package API transfer information
To see the changes, specify the
--dry-run flag; to apply
--apply; there is no default behavior for this command.
Building / Compilation
Launching a Dart application is extremely simple, just run the following command in the terminal:
$ dart run bin/myapp.dart
If you are inside a package and in the
bin directory there is a dart file with the same name as the package name, then the application can be done without specifying the file:
It is also possible to run applications from the packages specified in the dependencies to the current. For example, if your application has a dependency on the package
foo, to run a program in this package, just call the command:
$ dart run foo
Or specify a different program inside the
$ dart run foo:bar
Arguments and flags
Often when developing, you need to pass arguments to the
main() function, for this you need to pass them at startup after specifying the file:
$ dart run bin/myapp.dart arg1 arg2
You can also specify additional flags, for example, to debug the application:
$ dart run --enable-asserts bin/myapp.dart arg1 arg2
dart compile command allows you to compile a Dart program for the target platform. The output you specify with a subcommand can either include the Dart runtime or be a module (also known as a snapshot).
$ dart compile
||Executable||A standalone, architecture-specific executable containing source code compiled to native code and a small Dart runtime.|
||AOT module||An architecture-specific file containing source code compiled to native code, but does not contain the Dart runtime.|
||JIT Module||An architecture-specific file with an intermediate representation of the entire source code, as well as an optimized representation of the source code that was running during the training run of the program. JIT code may have higher peak performance than AOT code, but it depends on the training run.|
||kernel module||A portable intermediate representation of the source code. More|
Every program needs testing, this will reduce the number of errors during development and improve the quality of the application. For Python, there is an excellent framework that simplifies the work with tests, writing, and executing them - [Pytest] (https://docs.pytest.org/). Running tests with it is extremely simple:
The output of the command is quite detailed and makes it easy to understand where and what went wrong when running the tests. Here's what it looks like:
Testing in Dart is done with the
dart test command.
$ dart test
Several flags such as
-x) allow you to control which tests will be run. If several flags are specified, then tests that satisfy all conditions at once will be executed.
Python has a built-in
pip utility that allows you to easily manage packages, install, upgrade, and remove them. For more control, there are also third-party tools like poetry. Dart also has a tool that makes it easier to work with external dependencies - this is
$ dart pub
The possibilities of
dart pub are much wider than installing and removing packages. With it, you can manage the local package cache, publish packages to pub.dev, etc.
For example, consider installing a package in Python:
$ python3 -m pip install django
This command will install the up-to-date version of the Django package, however, it will not write it as a dependency, which means that on a new installation, you need to learn about this dependency somehow.
The same can be done in Dart like this:
$ dart pub add shelf
An important part of the development of applications and libraries is the documentation of functionality and source code. And for this, Dart has a special utility, which is extremely easy to run:
$ dart doc
Dart allows you to use comments and markup in your code to describe classes, functions, modules, and other structures. We'll look at these in more detail in a separate article, but for now, we'll mention that Dart handles special document comments. You can read about how to make documentation as effective as possible in the article Effective Dart.
We have reviewed some of the commands available using the
dart utility, some of them require a deeper understanding. However, even this cursory glance gives an idea of its capabilities and convenience available "out of the box" for the developer.
Next, we'll start diving into the Dart language and compare it to Python.