Python

Context managers and the `with` statement

Topics: with statement and context managers Updated 2020-10-05 Context managers and the with statement Similar to decorators, context managers are a concept many people use but only few understand. If you haven’t heard of the term ‘context manager’ before: you probably encountered them already while reading or writing from/to a file using the with statement. The most common use of context managers is the proper management of resources. In simple terms this means that we want to make sure that we open, read, write and close files correctly.

Tuesday, August 14, 2018 Read

The mysterious `if name == "main"`

Topics: What is if __name__ == "__main__" doing? I always wanted to dig into the statement if __name__ == "__main__" that is used in so many programs. I have used it for a long time already but until recently I had no idea what exactly it is doing. To make the topic as understandable as possible, I will divide the explanation into three steps. Step 1: Two ways of running code We saved our Magical Universe in a file named magical_universe.

Sunday, August 12, 2018 Read

Decorators within classes

Topics: Decorators within a class Updated 2020-10-05 After having talked about decorators already on day 5 and day 6 I would like to revisit the topic to discuss how decorators can be used within classes. Let’s put ourselves in the position of a Castle Kilmere member during the time the school is in war with Master Odon and his Dark Army. So these are dark, scary times. People at Castle Kilmere are constantly scared that something might happen to them, their family or their friends.

Saturday, August 11, 2018 Read

Immutable data classes

Topics: Immutable data classes Updated 2020-10-05 We have talked a lot about data classes in the last post. There is one further characteristic of data classes that I would like to study - immutability. We can make a dataclass immutable such that it fulfills the same purpose as typing.NamedTuple. To make a dataclass immutable we have to set frozen=True when creating the class. Let’s see how we can change our DarkArmyMember class from typing.

Friday, August 10, 2018 Read

Data classes

Topics: Data classes Updated 2020-10-05 Data classes are a feature that is new in Python 3.7. And taking a look at them is definitely worth it! Data classes According to the PEP on data classes, they are basically “mutable namedtuples with defaults”. We already looked at namedtuples on day 10 and 11. Namedtuples allow us to create an immutable class that primarily stores values (i.e. attributes). We used namedtuples for our DarkArmyMember class (because once you become a member of the dark army there is no way back.

Wednesday, August 8, 2018 Read

Abstract Base Classes

Topics: Abstract Base Classes, ABC’s Updated 2020-10-05 The last days I have been working on a lot of new classes and methods. Since they all belong to the same big concept, I decided to create one big post on the whole topic instead of several small ones. So let’s get right into it! Abtract Base Classes Up to now, our Magical Universe has a parent class (CastleKilmereMember) and several child classes (Pupil, Professor, etc.

Saturday, August 4, 2018 Read

Namedtuples

Topics: Immutable classes, namedtuples Updated 2020-10-04 Tuples Before looking at namedtuples, we should review what a tuple is. In Python, a tuple is a simple data structure that can be used for grouping arbitrary objects. Important to know is that tuples are immutable. That means that once a tuple has been created, it can not be changed anymore. We already used tuples in our Magical Universe. For example, we defined the pet attribute of the Pupil class to be a tuple:

Wednesday, August 1, 2018 Read

Duck typing, EAFP principle

Topics: Duck typing, EAFP principle Updated 2020-10-04 Duck typing Today we are going to look at some fundamental philosophies of programming: duck typing, EAFP and its opposite LBYL. Some of you may have heard of these principles already. However, because they are so fundamental we want to make sure that we apply them to our magical universe correctly. So what is duck typing? The most common saying regarding duck typing is “If it walks like a duck, and it quacks like a duck, then it must be a duck.

Tuesday, July 31, 2018 Read

Extending the Magical Universe

Topics: Adding new classes and methods to the Magical Universe Today I used some of the concepts introduced during the last days to extend my Magical Universe. Specifically: I added a classmethod for creating the ghost ’the mocking knight' I added a ‘friends’ attribute to the Pupil class I added methods for adding and listing all current friends of a Pupil I implemented a new Charm class that allows to create charms I added two classmethods for creating popular charms

Monday, July 30, 2018 Read

Underscore patterns for variable naming

Topics: underscore patterns for variable naming, _variable, __variable, __variable__, _ Updated 2020-10-04 Underscore patterns for variable naming Today we are going to look at a very important concept in Python: the usage of underscores when naming variables! In Python we have five different naming conventions that involve underscores. A variable with a single leading underscore like _elms This is a naming convention followed by most Python code A name prefixed with an underscore should be treated as a non-public part of the API and it might be changed without notice This holds independent of whether it is a function, a method or a data member A variable with (at least) two leading underscores and at most one trailing underscore like __my_private_variable

Sunday, July 29, 2018 Read

Properties, setter and getter methods

Topics: properties, @property and property(), setters, getters Updated 2020-10-04 Today, I digged a little deeper into the @property decorator, how it is related to the property() function and how its getter and setter methods work. These two links (link1, link2) were really helpful. Of course, there is also the official Python docs on the property() function. The @property decorator Yesterday we looked at decorators. The @property decorator allows us to create a read-only property.

Saturday, July 28, 2018 Read

Decorators

Topics: decorators Updated 2020-10-04 Today, we are going to look at decorators. Python’s decorators are an advanced concept so don’t worry if you don’t immediately understand how they work. The more you will use and read about them, the clearer the concept will become. I won’t go into too much detail here, so if you want to know more about decorators, take a look at Dan Bader’s website or the PEP on decorators.

Friday, July 27, 2018 Read