The Rise of SYDNI, or YAGNI is Only About Problems, Not Solutions

I’ve got a new programming methodology to propose. I call it SYDNI
(Sometimes You Do Need It). It is a response to the problems that I
see with YAGNI. In fairness, I don’t dislike YAGNI. In fact, I agree
with it 100% (well, maybe 95%). But to truly appreciate it, you need
a bit of context.


I’ve almost started thinking of YAGNI almost as a recursive way of
thinking. That is to say that I’ve begun to think of YAGNI as being
something that uses itself to implement itself. Allow me to explain.

What is YAGNI?

YAGNI stands for “you ain’t gonna need it.” I don’t want to make this post
an in-depth discussion of what YAGNI actually is, so click the
Wikipedia link if you aren’t familiar with YAGNI. The important thing
to take away from reading about YAGNI is that it’s saying that you
shouldn’t implement functionality if you don’t need it.


YAGNI sounds like a pretty straightforward way of thinking. And in a
lot of ways it is. But it’s more nuanced than one may think at first.
The “recursive” element of YAGNI that I speak of above is that YAGNI
(in my opinion) is a very specific solution to a very specific
problem, and that problem is over-engineering.

And YAGNI does its job well (especially in the context of Test Driven
Development). I tend to find myself throwing out a lot less code when
using YAGNI.

A lot of people take YAGNI to mean that the simplest solution is
always the best. That isn’t the case. Or at a very minimum, that
shouldn’t be the case. There’s a key thing about simplicity
that should be understood: it’s defined by the problem, not the
solution. This is key to understanding why YAGNI is so useful. Once
you’ve gotten to the point of choosing a solution, YAGNI is no help to
you. Thus, you have to use YAGNI to choose problems, not solutions.

You’re not in school anymore

In school, things are always so simple. You’re assigned a problem.
And you’re given a grade based on how well you solved that problem.
The real world is more complex.

You see, people too often forget that software developers don’t just
define solutions to problems. After all, aren’t all feature requests
nothing more than a statement of a problem? And isn’t choosing
software features a decision about what problems you will solve?

However, once you’ve chosen a problem to solve, there’s still the
issue of how to solve it.

Sometimes You Do Need It

In solving a problem, YAGNI’s usefulness starts to fade. It does have
some importance. You do have to make sure your solution is solving
the problem you set out to solve. However, beyond that, YAGNI just
doesn’t apply. In fact, it is likely harmful. That’s where SYDNI
comes in. Although SYDNI’s name is something of a jab at YAGNI, the
principle itself isn’t. Instead, SYDNI can be thought of as a
complement to YAGNI. A yin to YAGNI’s yang (alliteration for the

Oftentimes, thoughts may enter your head that start with something
like “we’ll never need…” or “this will never have to…”. This kind
of thinking is helpful when choosing the problem to solve. However,
it’s destructive when choosing a solution. In a couple of years,
there is only one thing that will be certain about the software you’re
writing: it will be different. And it will be different in ways you
can’t have predicted or imagined. If you’re using YAGNI
appropriately, you’re choosing the easiest problems to solve.
However, at least a few of these problems come out of left field.

Therefore, I would put SYDNI this way: ideally, a piece of software
will be no more simple or complex than the problem it is trying to
solve. Therefore, there is danger not only in solutions that are
overly complicated, but there is also danger in solutions that are
overly simple.

This leads to another conclusion: if SYDNI is followed appropriately,
the complexity of your source code is a direct measure of how complex
the problems it is solving are. The reverse is true as well. The
complexity of the problems you’re solving is a direct measure of how
complex your source code will be.

But I don’t live in an ideal world!

The key hole in SYDNI is the word “ideally”. Unfortunately, some
problems just don’t have perfectly compatible solutions. Therefore, a
key decision to be made is whether it is better to err on the side of
over-engineering or under-engineering a solution. We are now delving
into the realm of many disputes between programmers. Many people
(mis)educated on the arts of YAGNI will say that it is always better
to tend towards under-engineering. If this were true, YAGNI wouldn’t
be as useful to as many people as it has been.

Even more unfortunately, there is no “one size fits all” answer of
whether it is better to over-engineer or under-engineer. It is highly
situational and care must be taken to arrive at the appropriate
solution. If you don’t believe me, consider the following two

  1. Which life support machine would you rather be hooked up to?
    •  A machine whose software developers always did the simplest thing possible
    •  A machine whose software developers went out of their way to anticipate possible problems and planned for each of them
  2. Which one-page web app do you feel would be easiest to maintain?
    • An application that is implemented as two or three source files and a few database tables
    • An application with a highly normalized database, highly modular source, and great flexibility


I should hope that the answer to number 1 is obvious. And why it is
the correct answer should also be obvious: if you missed a particular
contingency, people can die. Thus, it makes sense to err on the side
of over-engineering.

But number 2 is a little bit less obvious (and maybe more debatable).
However, I would err on the side of under-engineering. After all, no
matter what changes come up, a one-page web app is still a one-page
web app. The worst case is that the app would be rewritten from
scratch. That’s not to say that you need to throw caution into the
wind and ignore normal good practice. Rather, it’s saying that it’s
not really a good idea to stress much over how maintainable that
application is.

Therefore, when deciding on a solution, there are two things that need
to be decided upon beforehand:

1. How complex the problem is.
2. Whether under-engineering is more harmful than over-engineering.

Once you get those two things squared away, it should be easy to get
an idea of how complex the solution should be.

The devil’s in the details

There are two schools of thought in the programming world:

  1. Explicit is better than implicit (configuration over convention)
  2. A developer should only have to program the unconventional aspects of a program (convention over configuration).

We’ll call #1 the Python school and #2 the Ruby school. In fact, I
would argue that this is an issue that’s at the core of whether code
is considered “Pythonic” or “Rubyic” (I doubt the last one is a word).

So which school of thought is right? I personally think they both
are. It doesn’t really take a whole lot to demonstrate that the
Python school of thought isn’t always right. Think about it. Did you
know that the Python runtime has a component that goes around deleting
objects from memory totally implicitly? How unpythonic is that?

The Ruby school of thought takes a bit more work though. After all,
if it’s unconventional, why should you have to configure it? Of
course, the problem here is in defining “conventional”. What’s
conventional to me is likely unconventional to others. And what’s
conventional to others could be unconventional to me.

I wish I had more advice on how to reconcile these two schools of
thought. The truth is that I struggle with them daily. But I think
having an intuition about this is the dividing line between
“experienced programmer” and “newb”. After all, if programming were
merely about “make everything explicit” or “make everything implicit”,
any idiot could do it.

I think this is also the core skill for writing readable code. You
need to determine what details are relevant to each piece of code.
Whatever the case, you need to make a conscious decision as to what
details shine through and what details you obscure. Because if these
things happen on accident, they’re almost guaranteed to be wrong.

My five rules for writing good code

I just came across a blog post that outlines 5 rules for writing good code.  I agree with them for the most part.  But this subject is extremely subjective and will vary from person to person.  Therefore, I’d like to write up my own rules for writing good code.

Keep it simple

This is the YAGNI rule.
There are often times when we want to try to solve problems we don’t have.  You must resist this urge.  It’s far easier to make simple code more complex than the other way around.  This is usually more of a challenge than it looks.  It’s a sign of good code that you constantly find yourself saying “any idiot could have put this together”.  Reality is that idiots only write simple code when the problem is easy or when they get lucky.

…but not simplistic

You can call this the SYDNI rule.
Albert Einstein said it best when he said “Everything should be made as simple as possible, but not simpler.”  I’ve seen too many “simple” hacks that ended up causing more of a maintenance problem than it would have been just to write something more complex.  As good a thing as simplicity is, you need to be realistic.  Don’t try to make a simple solution match a complex problem.

Abstraction is your friend

So what do you do in those situations where you need to use a complex solution?  Do you give up all hope and just write some horrible piece of crap?  No, you find a way to make that complexity easier to manage.  This is where abstraction comes in handy.
For instance, Lisp introduced the concept that “it’s all data”. This makes it easier to understand things.  If you want to know what something is, you already know that it’s data of some kind.  What is a function?  Data.  What is a list?  Data.  What is code?  Data.  This has a profound effect upon your ability to understand things.

Follow guidelines

Jeff Atwood would call this following the instructions on the paint can.  We tend to sneer at the idea of “best practices”, but reality is that they’re necessary.  There are a lot of problems out there that people have already dealt with and solved.  Why waste time not learning from others’ mistakes.

…but don’t worship them

As the old cliche tells us, rules were made to be broken.  Some of the most well known design patterns break the guidelines and have some of the worst code smells.  In fact, sometimes the guidelines conflict with each other.  Thus, don’t blindly follow guidelines without knowing their purpose.  Instead, understand the rules, know when to follow them and when following them is the greater of two evils.

How Celery, Carrot, and your messaging stack work

If you’re just starting with Celery right now, you’re probably a bit confused. That’s not because celery is doing anything wrong. In fact, celery does a very good job of abstracting out the lower-level stuff so you can focus just on writing tasks. You don’t need to know very much about how any of the messaging systems you’re using will work. However, to truly understand celery, you need to know a bit about how it uses messaging and where it fits in your technology stack. This is my attempt to teach you the things you need to know about the subject to be able to make everything work.


At the very bottom of celery’s technology stack is your messaging system, or Message Oriented Middleware in enterprise-speak. As of this writing, there are a couple of standards out there in this market:

  • AMQP – A binary protocol that focuses on performance and features.
  • STOMP – A text-based format that focuses on simplicity and ease of use.

Of course, there are a lot more players out there than just this. But these are the two protocols that are the most important to celery.

Now, a protocol is totally useless without software that actually implements it. In the case of AMQP, the most popular implementation seems to be RabbitMQ. The popular implementation of STOMP seems to be Apache ActiveMQ.


A good analogy that I think most people can wrap their heads around is the SQL database. STOMP and AMQP are like SQL, while RabbitMQ and ActiveMQ are like Oracle and SQL Server. Any one who has had to write software that works with more than one type of database knows how challenging this can be. Sure, it’s easy to issue SQL commands directly when you just support one type of database, but what happens when you need to support another? One possible solution is to use an ORM. By abstracting out the lower-level stuff, you make your code more portable.

The first thing most ORMs do is provide an abstraction to write SQL queries. For instance, if I want to write a LIMIT query for SQL Server, I would do something like this:

SELECT TOP (10) x FROM some_table

Oracle’s query would look something like this:

SELECT x FROM some_table WHERE row_num < 10

These are different queries, but they are both doing the same basic thing. That’s why SQLAlchemy allows you to write the query like this:

select([some_table.x], limit=10)

This is the functionality that carrot provides. Although most messaging systems are fundamentally different in a lot of ways, there are certain operations that every platform has some version of. For example, sending a message in STOMP would look like this:



AMQP’s version is binary, but would look something like this in text format:

basic.publish "hello" some_exchange a

Since we don’t want to worry too much about these protocols at a low level, carrot creates a Publisher class with a “send” message.


Carrot makes it so that we can forget about a lot of the lower-level stuff, but it doesn’t save us from the fact that we’re still working with a messaging protocol (albeit a higher-level one). Going back to the ORM analogy, we can see the same thing happening: we need a layer of abstraction to make dealing with different implementations of SQL easier, but we don’t want to write SQL. We want to write Python (or whatever your language of choice is).

Thus, ORMs will add another layer of abstraction. Wouldn’t it be nice if we could just treat a database row as a Python object? Or, in the case of task execution, wouldn’t it be nice if we could just treat a task as a Python function? This is where celery comes in. See, we could run tasks like this:

  1. Process A wants to run task “”
  2. Process A puts a message in queue saying “run”
  3. Process B sees this message and starts on it
  4. When done, Process B replies to Process A with the status.
  5. Process A acknowledges this message and uses the return result.

Rather than having to code all the details of the messaging process, celery allows us to just create a Python function “” that will do the above for us. Thus, we can execute tasks asynchronously without requiring that people reading our code know everything about our messaging backend.

Hopefully, this gives you a high-level overview of how celery is working behind the scenes. There are a lot of details that I’ve left out, but hopefully this provides you with enough knowledge that you can figure the rest out.

Tail Recursion in Python using Pysistence

A topic that occasionally comes up in Python development is that of tail recursion. Many functional programmers want to see tail recursion elimination added to the Python language. According to Guido, that ain’t gonna happen. And to be fair, I agree. Tail recursion can be tricky not only for new programmers, but for old timers as well.

However, that doesn’t mean that we need to give up on the concept altogether. This is a problem that is hardly new. Functional languages have been implementing tail recursion in environments hostile to it for a while now using a trampoline approach. Let’s see how the newest version of pysistence implements that algorithm:

def trampoline(func, *args, **kwargs):
    """Calls func with the given arguments.  If func returns 
       another function, it will call that function and repeat
       this process until a non-callable is returned."""
    result = func(*args, **kwargs)
    while callable(result):
        result = result()
    return result

This makes it much easier to implement things functionally (using pysistence’s functional lists):

def iter_to_plist(seq):
    seq = iter(seq)
    def inner(accum):
            return partial(inner, accum.cons(
        except StopIteration:
            return accum
    return inner(pysistence.make_list())

>>> trampoline(iter_to_plist, xrange(1000))
PList([999, 998, 997, 996, 995, 994, 993, 992, 991, 990, 989, 988, 987, 986, 985

That was more work than writing this in a language that does tail recursion automagically. But it wasn’t too bad now was it? Ultimately, I think this approach works for a few reasons:

  1. It’s explicit. The user is well aware of what’s happening because they’re returning a callable.
  2. It makes functional programming more natural. Instead of using true recursion and risking blowing the stack or converting this into a loop and continually reassigning to a variable, you can make the algorithm work without side effects.
  3. It lets Python stay imperative.

For me personally, this is a great set of arguments. I love Python and I love functional programming. The more functional programming I can do in Python, the better. But there are very few things in programming that are free, right? Here are some of the disadvantages:

  1. It’s ugly. I don’t deny this. But this alone is not an argument against it. If you are the kind of person who wants nothing but beautiful code, I’d argue that you’ve chosen the wrong language. Python tends to be beautiful when possible, but ugly when it has to be. Besides that this is the best you’re going to get without modifying the language itself or adding macros.
  2. It isn’t very performant. Insert your favorite quote about not needing to be blazing fast, just good enough here. Besides that, it can be optimized in C if need be.
  3. Who needs more ways to do functional programming? I’m not going to join any flamewars on this one. But I will point you to the advantages of functional programming in Python’s own functional programming HOWTO.

The other side of being a free electron

So my last blog post on the subject of free electon programmers seems to have been successful.  I’ve gotten responses in two forms:

  1.  This is so self-serving.  What about the other people on your team?  They have a special personality as well!
  2.  This really hit home with me.  But I still don’t really feel like it’s really helped me much.
My response to these points:  I couldn’t agree more!  Here’s the thing though:  it’s much more difficult to say what other people want.  On the other hand, what better expert is there on what you want than yourself?  That was kind of the idea behind my last post:  “if you’re struggling with somebody who has a personality like this, here’s what you need to understand”.
That said, I’ve learned a thing or two in my time that I think I can share.  Although this is mostly related to free electrons, a lot of this is useful for any programmer.

Other people have emotions

If I had to choose one area where INTPs and INTJs have the most difficulty, it’s here.  This goes beyond your typical geek social idiocy.  Heck, it hasn’t been more than a decade since it actually hit me that other people expect me to acknowledge their feelings.  Now I know this feels dumb.  And yes, you’ll still forget.  But you’d be surprised at how much this helps you get along with people.
You see, people expect you to react in certain ways when they say something.  When they tell you a story about something that’s exciting to them, show some interest no matter how inane it sounds.  When people are angry about something, empathize with them and try to find some common ground even if it’s difficult.  If it’s you they’re angry at, resist the temptation to respond in kind.  If you’re calm and rational about it, people will usually be willing to have a calm and civil discussion about things.
And this is the most important part:  if you did something wrong, apologize.  I know this can be hard, but if there’s one thing that’s never ceased to amaze me, it’s humankind’s capacity to forgive and forget.

It’s a good thing that other people don’t understand you

We’ve all been there before.  You have to spend an hour’s worth of your time explaining the simplest and most benign thing in the world to someone else who just doesn’t get it.  If the person is truly an incompetent idiot, you should be discussing things with your manager.  Otherwise, you should take the person’s bewilderment as a complement:  you understand something they don’t and they want to learn from you.  After all, if they really didn’t want to learn from you, they’d probably just ignore you.
In fact, you’d do well to take a page from their book.  Next time you find yourself feeling that someone else’s opinion is the stupidest thing ever, don’t criticize them.  At least not immediately.  Instead, ask questions to get at why it is they feel the way they do.  You never know, they could have seen something you haven’t.  You see, not only is it a good thing that people don’t understand you, but it’s also good that you don’t understand other people.

Fight the urge to always go it alone

Most of the time, it’s easiest for me to just go off on my own for a week or two, code something, and come back when it’s done.  The thing is that I almost always end up with something that nobody else really gets.  You don’t have to be joined at the hip with the entire team all the time.  But it’s helpful to just spend some time at least explaining your code to someone else.  This is good even if for no other reason than it helps you learn what trouble other people are going to have with it.
Code reviews are really awesome for this.

People like you

Yes, even when you’re being a jerk.  There have been several occasions where I’ve gotten into some rather heated arguments over mundane issues with people that were admittedly my fault.  And not once has anyone died because of it.  You see, if I had a choice between working with people who disagreed with everything I say or working with people who love all of my ideas, I’d go with the argumentative asshole every day.  People who think critically about other peoples’ ideas are a rare asset for a software company.  And your coworkers will appreciate this if they truly want to do their jobs.

Choose your battles

Free electrons have a very ordered way of looking at the universe.  We tend to get frustrated if something disturbs that way of thinking.  And that’s led me to some long arguments.
Next time you get into an argument with someone, ask yourself this:  “If I just let this person win, how big of a deal will it really be?”  If your answer is “not a big deal”, then just let them have their way.  If you can’t answer the question, then you probably are arguing over nothing and should let them have their way.
However, if your first instinct is “this is a huge deal” and you can explain why, then stick to your guns as much as possible.  Generally, people will be willing to cede the important fights to you if you stick to this strategy.


Admittedly, I’m borderlining on making free electron programmers the new “duct tape programmers”.  If that’s the case, then so be it.  If there’s one thing that nobody can say about Joel Spolsky’s piece on JWZ, it’s that people didn’t consider his way of thought.
However, I’d like to hear feedback.  What other piece of advice do you have for programmers like me?  Is there anything else that I’m missing or getting wrong?