Motivation Although Python has a ton of built-in features and the ecosystem is full of useful pip-installable packages sometimes you need to fire up some external tools os.system The simplest form of launching external tools is the os.system function import os os.system(“echo Hello from the other side!”) subprocess module The subprocess module is Python’s…
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…
Why principles? Every time you come to a fork in the road a principle can help you. Some examples: If traffic gets confusing, slow down, If you take the last pasta sauce from the pantry, put it on the shopping list The more you learn the more you earn Principles work as guiding lights but…
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.…
Resource Acquisition Is Initialization (RAII) is a programming idiom that describes how resource acquisition and deallocation should be tied to object lifetime. Wikipedia demonstrates how the C++ standard library implements this idiom using the types std::lock_guard<> and std::ofstream as examples. But is it really necessary to implement this idiom in every type you create? Can’t…
Motivation When writing Python packages you often have to assure that the packages can be used on different platforms and Python versions e.g. the package must work under Python 3.8 on Linux as well as with Python 3.9 on Windows. But how do you test all those supported OS and version combinations? Enter tox History…
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…
A horrifying amount of business is still driven by Microsoft Excel. Need some stats? Excel. Need some number crunching? Excel Most of the time you can work with formulas in your sheet and you will be fine. But sometimes you need more power: Time to level up your VBA skills History VBA stands for “Visual…