Motivation Sometimes you want to know how fast your code is. Before you start implementing a timer use the Python built-in timeit module. #measurewhatmatters Example Let’s take a simple function like a recursive implementation of factorial: def factorial(n): if n > 0: return n * factorial(n-1) else: return 1 If you want to test how…
In “What’s the difference between classmethod and staticmethod in Python?” we looked at static and class methods. The third big decorator is the @property decorator import pytest class Person: def __init__(self, name): self._name = name @property def name(self): print(‘Getting name’) return self._name @name.setter def name(self, value): print(f’Setting name to {value}’) self._name = value @name.deleter def…
Motivation pytest executes tests in a randomly order. Sometimes it can be useful to have a predefined order in which test cases can run. pytest has a neat plugin for this specific use case. Installation pip install pytest-order Usage import pytest @pytest.mark.order(1) def test_foo(): assert True @pytest.mark.order(2) def test_bar(): assert True @pytest.mark.order(3) def test_foobar(): assert…
Python comes with several built-in decorators. The most important are: @classmethod @staticmethod @property In a nutshell: A static method can be called on either an instance of the class or the class directly but cannot access any class member. A class method is basically the same but it can also access properties of the class.…
Motivation Sometimes a task which should be easy can be hard to accomplish in practice. Manipulating nested dictionaries in Python seems to be such a task. Without dotty Accessing nested dictionaries looks like this: data = { ‘a’: { ‘b’: { ‘c’: ‘d’ } } } assert data[‘a’][‘b’][‘c’] == ‘d’ You have to chain the…
Motivation Whether you need credentials to log into a system or some configuration parameters for your application, the .env concept might help you. Installation pip install python-dotenv Usage .env file Create an .env file in your project root folder You should not share this file or commit/push it to your version control. You should add…
When you’ve finished reading How to implement Python Decorators you might wonder if it is possible to hand over some parameters to the decorator function. And yes that is possible and can come in quite handy. For a Flask project I wrote a decorator to manage authorization of endpoints. I wanted to grant access to…
Motivation Sometimes you need to find files across multiple directories and / or directory hierarchies according to certain pattern. E.g. find all image files with the jpg extension You can use it to find files in a directory by using wildcard semantics. Let’s say we have a directory structure like this: glob_test/ |– dir_a/ |–…
What should you put into your __init__.py? Perhaps you already know that a python package is a directory which contains a __init__.py file In this article we will solve the mystery around the __init__.py For this article let’s assume the following project structure: Empty init file Sometimes doing nothing isn’t so bad at all. You…
Motivation Python decorators are a nice way to implement the decorator pattern. Perhaps you read the article about Python data classes and wondered how the @dataclass thingy worked. Example Let’s say we created the following function: def un_decorated_function(): print(‘–> Starting un_decorated_function’) print(‘Inside un_decorated_function’) print(‘<– un_decorated_function finished’) This works but violates the DRY principle if repeated…