DEV Community

Cover image for Why programming languages are slow
Vladislav Kopylov
Vladislav Kopylov

Posted on

Why programming languages are slow


Grigory Petrov from Evrone has a couple of fascinating talks on YouTube about programming languages. He had learned a lot about programming languages design and how compilers work under the microscope and he has found answers to questions about programming languages performance.

Here is my overview of his lectures (1, 2) in English. If you try to find an answer to the question of why Python or Ruby is slow, the article is for you.

The main question

Some people don’t want to learn and use Ruby, Python, etc because they have heard that these languages are slow. “Why do I need to use slow language” - they think. “It’s better to learn and use golang or javascript because I have heard they are fast.” Also, some junior programmers who have learned Ruby, Python worry about their choice. Did they make the right choice, because they have heard that the language is slow? Let’s find an answer to why some languages are slow.


Photo by Jeremy Zero on Unsplash

In order to describe how programming languages work we must begin with the CPU on a machine. Modern CPU has plenty amount of cores for its performance. Modern CPU architecture is challenging to learn and describe. In simple terms, we can say that the code execution speed is the amount of machine code instructions that one CPU core can exec by one moment.

CPU reads each instruction from memory. Read operation is always slow operation. Therefore each modern CPU hash multi-level cache (L1, L2, Ln cache) and processor registers. They help not to read data from memory.

In simple terms, code speed performance is equal to how effective our code (machine code) works with memory. Can we store data in CPU cache or do we have to read data from memory?

Take a look at languages

What programming languages as C, C++, Rust, Objective-C and Golang have in common? When a programmer writes code he always thinks about memory: we must specify the data type of each variable; we have to allocate memory in heap; always think about pointers, blocks; etc.

As an advantage, the source code will be compiled to machine code and it’s executed so fast. Nevertheless, everyone knows that write code in C, C++, Rust is challenging. It happens because the syntax is tricky and you have to always care about memory.

If a programmer/developer doesn’t want to worry about the memory he can delegate the routine to a compiler. A compiler is a tool that transforms your source code into machine code. it tries to do it effectively. Source code converted to machine code will be easily handled by the CPU and data will be stored in cache and registers

Programming languages as Java, C#, Javascript follow the way. When you write code in Java you don’t have to worry about memory because you delegate chores to a compiler.

Java, C#, Javascript have high-level and good-looking syntax. The code is still executed fast. Unfortunately, they have problems with extensibility. The compiler will convert source code and isolate the memory layer. It’s hard to write an extension for Java code or use third-party code written on C/C++. In order to write an extension designer had to implement an interface as Java Native Interface (JNI), but using it will decrease your code performance.

The third way is to delegate routine to runtime, virtual machine (VM). It means that the language will not compile source code to machine code, it will compile the source code to bytecode and execute the bytecode in VM. Programming languages as Python, Ruby, PHP follow the way. These languages have awesome high-level and sweet syntax and the ability to write an extension easy and fast. But the price of using a virtual machine is speed - code performance is slow.

Three skills

Photo by Lucas Santos on Unsplash

We can imagine each computer language as a character in a video role-playing game (RPG). In a typical RPG when we create a character we have a limited amount of points and few skills to put points into (strength, defence, intelligence, agility etc). Each language has three skills to put points into:

  • Speed - speed of execution
  • Syntax - enjoyable and elegant high-level syntax
  • Extensibility - memory compatibility in order to easy write and use third-party code or an extension.

When a person, group of people start to design a new programming language they can choose only two skills as the base. A third one will always be hard to achieve. For example, C, C++, Rust, Objective-C, Go are fast and have extensibility, but they have low-level inelegant syntax.

If a language is quick and has nice syntax - it will be hard to write an extension or use third-party code. Java, C#, Javascript are fast and have good high-level syntax. But, it’s hard to write an extension for Java code, or use third-party code written on C/C++.

Ruby, Python and PHP have chosen the third way. They have awesome sweet syntax, the code is easy to write. When you are writing the code you think only about business logic and don’t worry about memory. Also, it’s easy to use third-party code or write an extension as NumPy, SciPy in Python; or Nokogiri, Ruby-openCV, Redcarpet in Ruby. The price is performance these languages are slower than previous languages.


Photo by David Heslop on Unsplash

Whenever we say or hear that N language is slow remember that it was a meaningful decision in language design. You can ask a question: “How to became N language fast? Is it possible?”. Yes, it is possible but not easy to achieve.

Otherwise slow languages are flexible. It’s easy to write an extension in C++ and make some type of operation faster. For example NumPy and SciPy in Python. When we do ML in Python or use Ruby in order to write business login we use advantages of Python/Ruby in a high-level language and write the code fast. Also, we can delegate slow operation to swift extensions in third-party libraries in order to work with data, do math operations, parse text, etc.

Frankly speaking, nowadays Javascript is the only one language that tries to have all three skills. But it’s hard. It tries to spend all resources to be harmonious. I believe that in near future all modern languages will be in harmony will all three skills.

Top comments (17)

sucuturdean profile image

First of all, you keep saying that syntax is bad in c, c++ and Rust but that is very debateble, some may say that is better because it is more verbose/expresive, so don't just say that they have bad syntax, what you might have wanted to say is that they have a step learning curve because of the syntax. Second of all java and c# compile to byte code, not python and what other language you typed there. Python code runs on a program called interpreter which reads "raw" python code and executes it at the same time, that's why python is slow. Java and c# on the other hand, they use a compiler that produces byte code and you as the programmer distribute that byte code instead of the java or c# code you wrote. The difference between java like languages and c like languages is the code that is produced, the byte code is cross platform but needs a VW to run while the binary produced by c like languages is not cross platform but doesn't need a VW to run. That's why C like languages are the fastest, Java like languages are second fastest and Python like languages are the slowest.

kopylov_vlad profile image
Vladislav Kopylov • Edited

And I just want to clarify one point:

Second of all java and c# compile to byte code, not python and what other language you typed there.

Each modern interpreted language doesn't read and execute each line of the source code at the same time. Honesty they aren't "pure" compilation languages.

Starting with Ruby 1.9 the official Ruby interpreter implementation switched to YARV ("Yet Another Ruby VM"). It pre-compiles Ruby into bytecodes. Once Ruby source code is converted to bytecode, a VM executes the bytecode. Converting source code to bytecode gave significant speed advantages to Ruby.

Python source code is also compiled to bytecode. In Python, you can directly observe it in the .pyc files. In Ruby 2.6.0 we have Just-In-Time compiler (JIT). It compiles instructions that are used often into optimized binary which runs faster.

So these languages are a hybrid of compiled and interpreted code.

kopylov_vlad profile image
Vladislav Kopylov • Edited

Thank you for your comment. Yes, I agree that the syntax isn't "bad" (even I didn't use the word "bad"). In a university I enjoyed writing code on C, before I saw PHP and Python. But some people agree that it's challenging to write code and you always care about memory.

Grigory Petrov clarified it in the comment

sucuturdean profile image

You are saying both here and in your post that you allways have to think about memory in c, c++, rust and objective-c, but that is not true for c++ no more. With so many abstractions it has gotten hard to actually think about memory in that language. In rust its a similar story, but you have to worry about refrences instead of "memory".

aatmaj profile image

I always wondered about the syntax factor. If somehow we could be able to make C syntax simpler and easier to understand, that would be nothing like it! I think the Julia programming language is attempting the same. What are your thoughts upon his?

Also one more factor while choosing the language I feel important is the legacy of the language. Sometimes some programmers choose one language over the other simply because they are more acquainted with one, or compatibility issues.

grigoryvp profile image
Grigory Petrov

In the original lectures I elaborate on the "syntax" topic, unwinding it as "syntax that does not require developer to care about memory". In the end, "high level" and "low level" is how much you, as a software developer, need to "care" about memory. C and C++, abviously, requires such care. Go and Rust, on the other hand, require a DIFFERENT type of care. Still, they require it. While Python, Ruby, PHP, JS etc is "infinite clay" - you can operate on arrays, dicts and other data without concerning how they will layout in memory. Same for C# and Java.

aatmaj profile image

So true.

kopylov_vlad profile image
Vladislav Kopylov

Hi. Thank you for your question.

The article is only about language design and I accept the fact that there are a lot of reasons to choose a language. One more reason is a job factor. I had to learn PHP because many years ago I knew one company that hires junior developers.

Unfortunately I'm not familia with Julia, but thanks for your reference I will read more about it.

hebigami profile image

Rage start

Only someone with little to no experience in writing Rust could ever claim it's syntax is inelegant.

Rust's style is VERY different from C oder C++, not only due to it's unique rules but because it forces the programmer a lot to use what is commonly considered to be best practices (in a good way). A language that won't let you (easily) write crappy code isn't very approachable for juniors. But there is currently no more elegant language out there.

Rage end

kopylov_vlad profile image
Vladislav Kopylov • Edited

I'm sorry for this. Honesty, I had little experience with Rust. Grigory Petrov explained the moment about syntax in the comment

mtalijanac profile image
mtalijanac • Edited

Your usage of word syntax is just wrong. You could argue that a semantics of a language has an impact on speed because semantics puts constraints on compiler generated code. But to say that syntax has anything with speed is just wrong. Just look at for loop:

C, Java, C#:
for (int i = 0; i < 10; i++) 

(for-loop [i 0 (< i 10) (inc i)])     
Enter fullscreen mode Exit fullscreen mode

Completely different syntax. But which one is faster? The one with better compiler because semantics is the same and compilers don't care about syntax. Syntax is used to ease reading for humans. It is literally stripped out of code in compile pass. It means nothing in performance game.

Anyway all other points in article are wrong or badly phrased:

  • Like assuming inherit speed of language. Yes there is a speed to a language but you assume it is some kind of static property. It isn't.
  • Premise of being fast and low level somehow implies bad or lacking syntax. When in real world if C++ is of anything guilty: it is of too much syntax. And Rust and Go are pretty elegant for what they are.
  • And those conclusion about nice using extensions or JNI!? Just no.

So this article is just wrong. Like the complete body of article is build on wording and assumptions which are just wrong. With facts and conclusion which are wrong.

akygameru profile image

Dear author,

I think that you missed the point, of the question posed in the title, entirely while building your article.
Why, you might wonder?
First, you're trying to judge programming languages from the perspective of how good looking their syntax is. This is completely subjective and has no relevance. When you work long enough with a tool, you'll get used to its looks and whatever you thought about the looks in the first place will get dulled, even to the point of becoming beautiful.
Second, you're saying that the programmers are delegating the memory management to the compiler (with languages like Java, C#, JavaScript, etc.), which is wrong. For those languages the memory management is actually delegated to the runtime environment, aka VM - which all have, making life somewhat easier, but for certain use cases extremely heavy. One language that actually performs memory management, to some extent, during compile is Rust - there might be others, but, hey, I don't know them all :)
Third, you missed the mark with JNI (or however its equivalent in other languages is called). Using those is actually very fast and is also the reason why Java was able to achieve performances close to C/C++. Sure, writing such stuff is not as easy as pouring Java code, but, after all, it's not meant for every user.
Fourth, there are books out there teaching how to write a compiler. They are a very good read, and, daresay, a must for every developer, and they can help understand in better detail and in more depth what is going on in the insides.

My answer to your question is that in 9 out of 10 cases the guilty party is the programmer. Today we have crash courses claiming to teach you to write code in a matter of hours (some are more honest and make it weeks or months), but what they actually deliver is just another code gluer. Not anyone can be a musician for example, and as such not anyone can be a programmer, although is, by far, easier to become one.

Speed is not always the most important aspect, but choosing the right tool for your work definitely is. Besides, in programming, when speed is paramount, we always have machine code :)

yfchen123 profile image

"First, you're trying to judge programming languages from the perspective of how good looking their syntax is. This is completely subjective and has no relevance." Actually there are some languages that have horrible looking syntax that I would honestly avoid. Perl, Brainfck, Intercal, and Python come to mind.

osazemeu profile image
Osazeme Usen

Simplified and very explanatory. Thanks for sharing

aatmaj profile image

That is a real nice post!

Some comments may only be visible to logged-in visitors. Sign in to view all comments.