Two UNDERRATED Design Patterns 💡 Write BETTER PYTHON CODE Part 6

[@aneidlin]

Arjan, thank you so much! You are filling a void in programming tutorials. So many tutorials are way too basic, way too advanced, or way too light on details. And almost none of them go into the how or the why of design and architecture. There's a lot that you learn from just doing it, but you are hitting a sweet spot of advanced concepts without making me feel like a newbie. Your material is beyond beginner level and pre-expert, which is a difficult thing to accomplish, but you do it well. Thank you and keep it up!

[@kevon217]

^

[@absoluum]

Thank's for the videos Arjan. I've been programming with python for about a year with no formal training, and hearing about these methods and seeing examples have been very beneficial.

[@ArjanCodes]

Glad that you like them and that it helps you!

[@diegol_116]

I am an industrial engineer from Colombia, I study programming in a self-taught way and I am enormously grateful for the content you upload...

[@doublegdog]

One of the most underrated youtube channels out there. Great informative videos! I am a senior engineer and it is always nice to expand my knowledge, even if I have forgotten a lot of these.

[@ArjanCodes]

Thank you so much, glad you like it!

[@ArjanCodes]

I'm wondering: did any of you use one of these two patterns in your code recently? Let me know!

[@stevev469]

Me! Implementing the Bridge as a final assignment when following your course system development methods. Great to see my former teacher making clear KZbin videos about complex subjects. Passed with a 7.5!

[@ArjanCodes]

Yes! - and I can officially confirm you got that grade without bribing anyone ;).

[@stevev469]

@@ArjanCodes Phew that was a close call😅 Ps: Great videos by the way. You must have practised alot with the sound effects during that course. Looking forward to an abstract factory sound effect reference😉 Keep going!

[@ArjanCodes]

Thanks Steve! I did learn a lot about video editing since teaching that course, so I hope things are a bit less "cringeworthy" this time around 😂

[@bubblefoil]

No, but I had to maintain a codebase full of template methods and learned the hard way that it is the worst of all programmer's nightmares. It should be listed as an anti-pattern because it basically validates sharing code via inheritance. Never ever re-use code via inheritance. We have composition for this purpose.

[@PavloOrynchak]

Wow! Arjan, thank you very much! I've started rewriting my code using your advices already after second video in your channel. This channel is a gem! Exactly what I have been missing for years!

[@ArjanCodes]

Glad to hear the videos are helpful to you!

[@ke30_]

Very cool, thank you! I would love to see more design patterns explained by you

[@ArjanCodes]

Thanks Kevin, glad you like it + there’s more in the pipeline 😉.

[@matsim0]

Thanks again Arjan! I really liked the "Head first design patterns" book (which I bought some time ago in a HumbeBundle sale). But I've not yet actually worked through all the examples, because while it is explained excellently, the examples are somewhat more involved than yours (and they are in Java...). Your examples on the other hand are reduced to the minimum which I like very much - it is a joy to just go along with them and try them out while following the video.

[@ArjanCodes]

Thanks matsim0, glad you like the examples!

[@UgoAno]

First time commenter. Your tutorials are outstanding and clear. You are helping me in a different way. I find I implement a lot of these patterns by attempting to be as SOLID as possible. But you're highlighting what those patterns are and their names. I'm going to recommend the people I manage to watch your videos.

[@sergioquijanorey7426]

This video was pure gold. Thanks for explaining two complicated patterns for me with such a good example,

[@ArjanCodes]

Thank you Sergio, happy you liked it.

[@ryanperkins3929]

I've come to consider you one of my primary instructors. Thanks for your presentations.

[@davia.sampaio8633]

I just discovered your channel and I'm without words to express my love for your work. Thank you very much

[@ArjanCodes]

Glad to hear you like the videos!

[@PillesPlace]

You run the best python channel that I know of. Many thanks for this education!

[@ArjanCodes]

Thanks so much, glad the content is helpful!

[@ulrickpspgo]

Hi! I came across one of your videos and couldn't stop watching for 3 hours! You provide such an interesting information! Thanks a lot for your effort. You earned a new subscriber!

[@JackReacher1]

I like the clarity that you have when you explain the design pattern. Most of the other people who understand them don't actually explain it well. Thank you

[@ДмитрийДобровлянский]

Hello from Russia! Thanks a lot for your lessons! Very practical material! Your chanel is great!

[@ArjanCodes]

Thank you very much, glad you like the content!

[@viniciusmeireles6267]

This channel is PURE GOLD! I think this two patterns will help me in my current project. I'll try to implement it in my code right now! Needless to say that I've subscribed and liked lol

[@ArjanCodes]

Thank you - glad to hear the videos are helpful to you!

[@GuRuGeorge03]

I am in the 2nd week of my software engineering job now and there are tons of patterns in the huge code base that are being used and I love analyzing them and sometimes I even find ways to improve the patterns, in part thanks to your videos :)

[@ArjanCodes]

Good to hear the videos are helpful to you. And good luck with your new job!

[@lioneluran]

Thank you Arjan! I've been programming for a while, now, but I'm self-taught and never heard about design patterns until very recently, with this series. Can't really see the difference between the Template and Strategy design patterns. They both use abstract classes depicting a backbone of abstract methods that are later defined in the actual class implemeting the non-abstract method. I'd love to see a video disambiguating these two, if you think it's appropriate. Cheers a keep up this great work!!

[@watashiwan]

Really good explanation about the importance of design pattern. I can’t agree you anymore.

[@coert]

Hey Arjan, just finished a cloud metrics and measurements implementation using your ABC/abstractmethod examples. Thanks for the great videos and explanations!

[@ArjanCodes]

Hi Coert! Good to meet you here 😊. And happy that the examples were helpful.

[@EW-mb1ih]

Thank you for your video! I don't get exactly what the templast design pattern do but I like the bridge pattern which looks like an extension of the strategy pattern.

[@govindasharma8619]

Why don't you write a book for design patterns in python? There may be 50 books out there but we all like how you explain and demonstrate with practical examples.

[@t6u934]

You’re a great teacher! Thanks for all these videos.

[@ArjanCodes]

Thank you! Glad you like the videos!

[@Formulka]

it's hard to build larger projects without these patterns, at least if you care about your sanity, very nice explanation and the sneaky semicolon is becoming a meme :)

[@ArjanCodes]

;

[@ArjanCodes]

Perhaps I should hide a semicolon in my next videos and see who finds it first :).

[@michaelhart8928]

Arjan, these videos have been fantastic. I actually just left a role as an HFT (funny enough watching a trading example) and wanted to brush up on my python, given I have been primarily using Java for the past five years exclusively. Funny enough, the last video on event based systems (observer pattern) is a great use case for an HFT trading system!

[@murghay01]

If I may ask a question: I am creating a little application to start understanding which behavioral design pattern makes more sense. I make calls to any API. There are basically two functionalities that it has, First, on a 200 response, the JSON will get the id, user, personal information of a character. Second, there is a second key in the JSON response that will ultimately make a second request and do things. Both scenarios lead to adding values into the DB, but two different tables. I can't quite tell which would make sense: Chain of Responsibility Pattern, Template, maybe even Strategy (but I dont think this one). What makes one far more excellent than the other. Honestly, all of the behavioral design patterns seem like a riff of one another.

[@ArjanCodes]

What I would suggest is to start from the principles instead of the patterns. What function has what responsibility (cohesion) and how are they coupled? Then, imagine how each pattern changes that. Any of these patterns may work considering what you describe, but the way data is stored and used in your code also plays a big role (especially for coupling), so some patterns will probably lead to a better result in terms of reduced coupling and strong cohesion.

[@murghay01]

@@ArjanCodes thank you very much

[@diegorodriguezv]

Great videos! Thanks. A heads up: The code coverage video is missing from the Software Design in Python playlist.

[@TimGrob]

I have not fully understood what's the difference between the method template pattern and the strategy pattern. The two look very similar. Can you tell me the difference once more? Thank you.

[@jufenico]

This is great mate! I'm forcing myself to learn oop coming from functional and this is exactly what I was looking for. Your videos explain the concepts which is super helpful to understand and implement

[@ArjanCodes]

Glad you liked it, Juan!

[@shashishekhar----]

Arjan you are a true Guru , 🙏👌

[@michalzdanowicz2816]

It's a pleasure to watch your videos. Thanks for sharing your knowledge.

[@ArjanCodes]

Thanks Michal, happy you’re enjoying the content!

[@grzegorzryznar5101]

I like format of these videos very much! Practice combained in really good way with theory :)

[@JorisNonnast]

May I ask, what is the difference between the bridge pattern and dependency injection?

[@bonmec101]

That there is association on abstract class level?

[@SweetSummerChildern]

Hi Arjan! I have watched your video of Strategy pattern. I felt the template pattern is quite similar. I don't understand the diffrence.

[@JohnMatthew1]

Thank you for all your videos, you have a very nice presentation and make it so easy to understand.

[@ArjanCodes]

Thank you John, glad you like the videos!

[@rsrini7]

Thanks. Unknowingly i used both the patterns in my code.

[@Ejik53]

Very good channel ,with good explanation and examples, thanks a lot!

[@sreddy1024]

Thank you, Arjan, for the great explanation. Is it correct to say that, "bridge design pattern is made of dependency inversion"?

[@robertbrummayer4908]

Excellent quality as usual. Great job!

[@MrTrebor2]

Python's world like to do things in "pythonic" way. Design patterns are a next step game changer. Template (state), bridge, observer/pubsub patterns + asyncio -> critical mass to build complex trading bots in a simple and managable way. East or west Arjan is the best!

[@taneliharkonen2463]

This was veeeeeery useful! :D Not very often u see people go explaining useful design patterns or techniques in utube. People go ooonanooon about frameworks and such, which is not that useful in learning. Frameworks come and go... design patterns and techniques dont! :o

[@davidsyengo1893]

Amazing vid. The bridge pattern implementation seems to work similar to the proxy pattern.

[@ArjanCodes]

Glad you enjoyed the content!

[@Karujin277]

Hello Arjan, thank you for the videos. Compared to these patterns you have used on the video what do you think of completely seperating the exhange and trader classes where you would get the prices from exhange class and then you would call the check prices method with a list of prices. That way you control what you want to pass and also you don't need mock exhange objects to test your trader. You just need a list of prices.

[@ArjanCodes]

Thanks! Good suggestion. Most design patterns focus on separating things by looking at behavior. What you suggest is an alternative which separates things by data. This can be really helpful and is commonly used in for example REST APIs that separate different components of an application by (JSON) data.

[@Megosks]

Thank you very much! I have actually used those a lot but I've never knew how they are named :D

[@Han-ve8uh]

At 14:20 you were editing the Trading strategy and Exchange source code to change it's behaviour, Practically should this really be done? It feels really clunky. This video tells us to open the python file and edit it everytime we want to change some details, but I was expecting changes to be made through command line arguments during script calling with something like argparse to parse the selections.

[@vladyn2522]

Brilliant video series! thank you so much for making it available and accessible!

[@ArjanCodes]

Thank you, glad you like the videos!

[@SM-vg6xk]

You're awesome. Please don't stop making videos

[@ArjanCodes]

Thanks!

[@talibuddeenabdulhakeem]

If you were building an application. Would you keep all of these classes in one file? Also when you would start breaking you code into multiple files or modules? I struggle on when I should break something into another file because of too many classes. For example would averageTrader become its own module at some point and you have all the abstract base classes in one module... Maybe I am overthinking.. Thank you for the content, I have loved all your videos so far!

[@ArjanCodes]

Thanks, glad you like the videos! I would definitely put each class in a separate file (including abstract classes). That also makes it much easier to find them later on when your codebase grows larger. The only reason I'm keeping everything in a single file here is that I don't have to switch to another view in the video.

[@jasongen]

Thank you for the video! But what is the difference between Bridge and Dependency Injection?

[@amnanajib8167]

The template pattern seems to me very close to the strategy pattern presented. What is the fine difference?

[@dennbauer]

Great video!! I like the way you explain with simple Examples - super cool. One question on bridges: let's assume I have to bridge over three abstract classes - in your Example maybe a Bot, an Exchange and a Trading Indicator. Would you rather build a fourth abstract class and use it as a bridge or would your bridge two classes from one? in case of the latter: How to decide which one to put in the "middle"? Hope the question makes any sense at all :-)

[@jonasj.1264]

Discovered your Videos about a week ago, absolutely love them! ❤ They may be the same principles i should already know from university, but ur examples and explanations definitly improved my understanding of them. Already recommended your channel to some fellow students 😀 In regards to this video, the bridge pattern seems to be very much in line with the whole composition principle, isnt it?

[@ArjanCodes]

Thank you Jonas! Yes - the Bridge pattern is a great example where composition is applied tastefully.

[@vivek77]

Hello Arjan, First of all thanks for the work you are doing, I really enjoy your content and look back into my code and wonder why I didn't know this earlier. I can image it takes a lot of time and effort to create videos of this quality. Would you also through some light into factory pattern and when it is ok to follow this pattern ? Wishing you all the luck in reaching 10k subscribers soon.

[@ArjanCodes]

Hi, thank you very much, I’m happy you’re enjoying the videos. Factory pattern is definitely something I’m going to cover soon.

[@fuuman5]

Congratz to 1k subscriber!

[@ArjanCodes]

Thank you! I’m still looking in disbelief at that number...

[@fuuman5]

@@ArjanCodes You deserve it. This is just quality content. I am a professional developer for years and I would still watch basic videos from you just because you explain it so well :D Love from germany!

[@kotslike]

nice example Arjan! Well done :)

[@ArjanCodes]

Thanks a lot!

[@bokistotel]

I still do not understand when should I use Strategy and when should I use Template?

[@munkh-odjargalsaikhan258]

Good stuff! I wonder for a trading bot, which class shall be responsible for calculating position sizes and stop losses in this template? the bot or the exchange?

[@christianwooldridge406]

bot

[@RileyGein]

I would love to see this series recreated for Golang

[@thygrrr]

At the time the video was released, indeed the best strategy would have been to sell bitcoin. :D I never heard of this pattern as "Template Method", I only know this as basic inheritance and the "Bridge" is what I know as the Strategy Pattern.

[@dansmar_2414]

THE BEST CHANNEL!!

[@ArjanCodes]

Thank you!

[@CarlosMorenoV]

My favourite design pattern: Template!

[@ArjanCodes]

Thanks so much Carlos, glad the content is helpful!

[@imadetheuniverse4fun]

I feel like I'm bugging you since I'm just going through all your content in order 🤣. I'm really getting a lot out of it! My question for this one: Do you think that the `typing.Protocol` class can be used here instead of / or in addition to the `abc.ABC` classes? For example with the `Exchange` class, it doesn't hold any data, it only contains methods (unlike the `TradeBot` class which contains a reference to an exchange). Would it be a good idea to instead define the exchange as `class Exchange(trading.Protocol)` ? (I only ask out of curiosity because I'm just learning about these things) Thanks again for the great content!

[@ArjanCodes]

Glad you like the content, and yes, that’s certainly a possibility. In fact I think in some more recent videos I come back to the trading/exchange example and use protocols there.

[@imadetheuniverse4fun]

@@ArjanCodes Good to know, looking forward to it.

[@pablovirus]

Very interesting patterns and excellet video as usuas, thanks!! If only I had a job where I could use them now lol

[@ArjanCodes]

Thanks so much, glad the content is helpful!

[@ShanilPanara]

Absolutely loved this. So well explained. Thank you 💜

[@ArjanCodes]

Glad it was helpful!

[@tbtitans21]

What about a class init from dictionary of buy/sell methods? HODL_strategy = { 'buy': lambda price: price < 10000000, 'sell': lambda price: False, } Saves some lines init_from_dict(HODL_strategy)

[@ArjanCodes]

Sure, that would work, and this is perhaps a bit shorter. On the other hand, classes allow you to define more strictly what method names should be called, which parameters each method has, etc. That is helpful, especially if you're working in a team.

[@talibuddeenabdulhakeem]

this is cleaver haha, Reading something like this would make me go crazy if it was in my code base

[@jonathanheadley2729]

Love your videos!

[@ReRubis]

Love this channel. :)

[@proud22beme]

how does bridge pattern differ from composition? both seem to do the same thing, pass a instance of a class implementing the ABC to the object that needs to use it

[@ArjanCodes]

Composition simply means that an object uses or contains another object. The Bridge pattern is a design pattern that uses composition, but in a very specific way: the composition occurs at the abstract base class level. As a result, the Bridge pattern allows you to have two hierarchies of classes that can vary independently, with a bridge (= a composition) to connect the two.

[@proud22beme]

EDIT: nvm, i got it, just took some time to understand fully @@ArjanCodes so to try to summarize, bridge is a extension of composition where A needs to access B, but B is not in the same hierarchy, and A does not need to know directly about B. so C is created as a ABC class with generic methods (read, write, ect). and when C is created it is passed a refence to what to what it bridges to, so A calling C.read() is actually calling B.read() but A does not know that, it only knows that C.read() exists? hope that makes sense

[@ArjanCodes]

Exactly- with the addition that A itself is also an abstract class. As a result subclasses of A use subclasses of C without any of the subclasses on both sides knowing about the other instance. For example, A could be the top of a hierarchy of player characters in a game, and C could be the top of a hierarchy of graphics engines. The bridge would allow you to render Mario on iOS and Luigi on Android or any other combination of a specific character + graphics engine.

[@guanahmed9804]

Help please; I have made a web crawler python projet and still not sure which design pattern shall I follow in web scraping case.

[@ArjanCodes]

Hi! Feel free to ask your question in the Discord server: discord.arjancodes.com. Perhaps someone can help you there.

[@Victorinoeng]

From my personal experience, I have leveraged the template pattern for web scrapers before. All my web scrapers had a very similar ETL process, but the actual Transform step could vary vastly based on the data/data source being scrapped. Hence I defined a base/template with the main generics methods and transform as abstractmethod In my experience, that was a great way to minimize amount of code, apply DRY, and yet have a very flexible approach

[@DRanduletti]

it was a beautiful time year ago when stock moved faster then a Tesla Model S... Anyway thank you a lot! PS: i havent realised that i use Bridge pattern, i just called it compositin)

[@maxitorres7]

LOve it! Thanks a lot!

[@ArjanCodes]

Glad you like it!

[@babatumises.r.o.5568]

Hi, will you have some premium content, i realy like your channel and content is very cool quality. Are you specialized only to python? What about PHP, Java, C#, C++, NVCC?

[@some84884]

Nowadays, it's clear that your predictor was right ad it was better to sell Bitcoin that time :D

[@realKeiichiArt]

Great!! Thank you very much! :)

[@ArjanCodes]

You’re welcome - glad you enjoyed the video!

[@kopytko998]

I don't know how much money you earn, but it is not enough. Thank you!

[@ArjanCodes]

Thank you Andrzej, glad you like the videos!

[@sandorbakos2929]

Amazing :)

[@ArjanCodes]

Thanks! 😄

[@DuyTran-ss4lu]

Cool!

[@CrapE_DM]

I just find it weird that you kept saying "strategy" while talking about Template. I would prefer a Strategy pattern, personally. And then your use of the Bridge pattern is actually more of a Strategy pattern

[@mariolim96]

Bridge pattern seems like factory pattern