As a co-designer of one of the world's most popular programming languages, one of the more frustrating behaviours I regularly see (both in the Python community and in others) is influential people trying to tap into fears of "losing" to other open source communities as a motivating force for community contributions. (I'm occasionally guilty of this misbehaviour myself, which makes it even easier to spot when others are falling into the same trap).

While learning from the experiences of other programming language communities is a good thing, fear based approaches to motivating action are seriously problematic, as they encourage community members to see members of those other communities as enemies in a competition for contributor attention, rather than as potential allies in the larger challenge of advancing the state of the art in software development. It also has the effect of telling folks that enjoy those other languages that they're not welcome in a community that views them and their peers as "hostile competitors".

In truth, we want there to be a rich smorgasboard of cross platform open source programming languages to choose from, as programming languages are first and foremost tools for thinking - they make it possible for us to convey our ideas in terms so explicit that even a computer can understand them. If someone has found a language to use that fits their brain and solves their immediate problems, that's great, regardless of the specific language (or languages) they choose.

So I have three specific requests for the Python community, and one broader suggestion. First, the specific requests:

If we find it necessary to appeal to tribal instincts to motivate action, we should avoid using tribal fear, and instead aim to use tribal pride. When we use fear as a motivator, as in phrasings like "If we don't do X, we're going to lose developer mindshare to language Y", we're deliberately creating negative emotions in folks freely contributing the results of their work to the world at large. Relying on tribal pride instead leads to phrasings like "It's currently really unclear how to solve problem X in Python. If we look to ecosystem Y, we can see they have a really nice approach to solving problem X that we can potentially adapt to provide a similarly nice user experience in Python". Actively emphasising taking pride in our own efforts, rather than denigrating the efforts of others, helps promote a culture of continuous learning within the Python community and also encourages the development of ever improving collaborative relationships with other communities. Refrain from adopting attitudes of contempt towards other open source programming language communities, especially if those communities have empowered people to solve their own problems rather than having to wait for commercial software vendors to deign to address them. Most of the important problems in the world aren't profitable to solve (as the folks afflicted by them aren't personally wealthy and don't control institutional funding decisions), so we should be encouraging and applauding the folks stepping up to try to solve them, regardless of what we may think of their technology choices. If someone we know is learning to program for the first time, and they choose to learn a language we don't personally like, we should support them in their choice anyway. They know what fits their brain better than we do, so the right language for us may not be the right language for them. If they start getting frustrated with their original choice, to the point where it's demotivating them from learning to program at all, then it makes sense to start recommending alternatives. This advice applies even for those of us involved in improving the tragically bad state of network security: the way we solve the problem with inherently insecure languages is by improving operating system sandboxing capabilities, progressively knocking down barriers to adoption for languages with better native security properties, and improving the default behaviours of existing languages, not by confusing beginners with arguments about why their chosen language is a poor choice from an application security perspective. (If folks are deploying unaudited software written by beginners to handle security sensitive tasks, it isn't the folks writing the software that are the problem, it's the folks deploying it without performing appropriate due diligence on the provenance and security properties of that software)

My broader suggestion is aimed at folks that are starting to encounter the limits of the core procedural subset of Python and would hence like to start exploring more of Python's own available "tools for thinking".

Broadening our horizons One of the things we do as part of the Python core development process is to look at features we appreciate having available in other languages we have experience with, and see whether or not there is a way to adapt them to be useful in making Python code easier to both read and write. This means that learning another programming language that focuses more specifically on a given style of software development can help improve anyone's understanding of that style of programming in the context of Python. To aid in such efforts, I've provided a list below of some possible areas for exploration, and other languages which may provide additional insight into those areas. Where possible, I've linked to Wikipedia pages rather than directly to the relevant home pages, as Wikipedia often provides interesting historical context that's worth exploring when picking up a new programming language as an educational exercise rather than for immediate practical use. While I do know many of these languages personally (and have used several of them in developing production systems), the full list of recommendations includes additional languages that I only know indirectly (usually by either reading tutorials and design documentation, or by talking to folks that I trust to provide good insight into a language's strengths and weaknesses). There are a lot of other languages that could have gone on this list, so the specific ones listed are a somewhat arbitrary subset based on my own interests (for example, I'm mainly interested in the dominant Linux, Android and Windows ecosystems, so I left out the niche-but-profitable Apple-centric Objective-C and Swift programming languages, and I'm not familiar enough with art-focused environments like Processing to even guess at what learning them might teach a Python developer). For a more complete list that takes into account factors beyond what a language might teach you as a developer, IEEE Spectrum's annual ranking of programming language popularity and growth is well worth a look.

Procedural programming: C, Rust, Cython Python's default execution model is procedural: we start at the top of the main module and execute it statement by statement. All of Python's support for the other approaches to data and computational modelling covered below is built on this procedural foundation. The C programming language is still the unchallenged ruler of low level procedural programming. It's the core implementation language for the reference Python interpreter, and also for the Linux operating system kernel. As a software developer, learning C is one of the best ways to start learning more about the underlying hardware that executes software applications - C is often described as "portable assembly language", and one of the first applications cross-compiled for any new CPU architecture will be a C compiler Rust, by contrast, is a relatively new programming language created by Mozilla. The reason it makes this list is because Rust aims to take all of the lessons we've learned as an industry regarding what not to do in C, and design a new language that is interoperable with C libraries, offers the same precise control over hardware usage that is needed in a low level systems programming language, but uses a different compile time approach to data modelling and memory management to structurally eliminate many of the common flaws afflicting C programs (such as buffer overflows, double free errors, null pointer access, and thread synchronisation problems). I'm an embedded systems engineer by training and initial professional experience, and Rust is the first new language I've seen that looks like it may have the potential to scale down to all of the niches currently dominated by C and custom assembly code. Cython is also a lower level procedural-by-default language, but unlike general purpose languages like C and Rust, Cython is aimed specifically at writing CPython extension modules. To support that goal, Cython is designed as a Python superset, allowing the programmer to choose when to favour the pure Python syntax for flexibility, and when to favour Cython's syntax extensions that make it possible to generate code that is equivalent to native C code in terms of speed and memory efficiency. Learning one of these languages is likely to provide insight into memory management, algorithmic efficiency, binary interface compatibility, software portability, and other practical aspects of turning source code into running systems.

Object-oriented data modelling: Java, C#, Eiffel One of the main things we need to do in programming is to model the state of the real world, and offering native syntactic support for object-oriented programming is one of the most popular approaches for doing that: structurally grouping data structures, and methods for operating on those data structures into classes. Python itself is deliberately designed so that it is possible to use the object-oriented features without first needing to learn to write your own classes. Not every language adopts that approach - those listed in this section are ones that consider learning object-oriented design to be a requirement for using the language at all. After a major marketing push by Sun Microsystems in the mid-to-late 1990's, Java became the default language for teaching introductory computer science in many tertiary institutions. While it is now being displaced by Python for many educational use cases, it remains one of the most popular languages for the development of business applications. There are a range of other languages that target the common JVM (Java Virtual Machine) runtime, including the Jython implementation of Python. The Dalvik and ART environments for Android systems are based on a reimplementation of the Java programming APIs. C# is similar in many ways to Java, and emerged as an alternative after Sun and Microsoft failed to work out their business differences around Microsoft's Java implementation, J++. Like Java, it's a popular language for the development of business applications, and there are a range of other languages that target the shared .NET CLR (Common Language Runtime), including the IronPython implementation of Python (the core components of the original IronPython 1.0 implementation were extracted to create the language neutral .NET Dynamic Language Runtime). For a long time, .NET was a proprietary Windows specific technology, with mono as a cross-platform open source reimplementation, but Microsoft shifted to an open source ecosystem strategy in early 2015. Unlike most of the languages in this list, Eiffel isn't one I'd recommend for practical day-to-day use. Rather, it's one I recommend because learning it taught me an incredible amount about good object-oriented design where "verifiably correct" is a design goal for the application. (Learning Eiffel also taught me a lot about why "verifiably correct" isn't actually a design goal in most software development, as verifiably correct software really doesn't cope well with ambiguity and is entirely unsuitable for cases where you genuinely don't know the relevant constraints yet and need to leave yourself enough wiggle room to be able to figure out the finer details through iterative development). Learning one of these languages is likely to provide insight into inheritance models, design-by-contract, class invariants, pre-conditions, post-conditions, covariance, contravariance, method resolution order, generic programming, and various other notions that also apply to Python's type system. There are also a number of standard library modules and third party frameworks that use this "visibly object-oriented" design style, such as the unittest and logging modules, and class-based views in the Django web framework.

Object-oriented C derivatives: C++, D One way of using the CPython runtime is as a "C with objects" programming environment - at its core, CPython is implemented using C's approach to object-oriented programming, which is to define C structs to hold the data of interest, and to pass in instances of the struct as the first argument to functions that then manipulate that data (these are the omnipresent PyObject* pointers in the CPython C API). This design pattern is deliberately mirrored at the Python level in the form of the explicit self and cls arguments to instance methods and class methods. C++ is a programming language that aimed to retain full source compatibility with C , while adding higher level features like native object-oriented programming support and template based metaprogramming. It's notoriously verbose and hard to program in (although the 2011 update to the language standard addressed many of the worst problems), but it's also the language of choice in many contexts, including 3D modelling graphics engines and cross-platform application development frameworks like Qt. The D programming language is also interesting, as it has a similar relationship to C++ as Rust has to C: it aims to keep most of the desirable characteristics of C++, while also avoiding many of its problems (like the lack of memory safety). Unlike Rust, D was not a ground up design of a new programming language from scratch - instead, D is a close derivative of C++, and while it isn't a strict C superset as C++ is, it does follow the design principle that any code that falls into the common subset of C and D must behave the same way in both languages. Learning one of these languages is likely to provide insight into the complexities of combining higher level language features with the underlying C runtime model. Learning C++ is also likely to be useful when using Python to manipulate existing libraries and toolkits written in C++.

Array-oriented data processing: MATLAB/Octave, Julia Array oriented programming is designed to support numerical programming models: those based on matrix algebra and related numerical methods. While Python's standard library doesn't support this directly, array oriented programming is taken into account in the language design, with a range of syntactic and semantic features being added specifically for the benefit of the third party NumPy library and similarly array-oriented tools. In many cases, the Scientific Python stack is adopted as an alternative to the proprietary MATLAB programming environment, which is used extensively for modelling, simulation and numerical data analysis in science and engineering. GNU Octave is an open source alternative that aims to be syntactically compatible with MATLAB code, allowing folks to compare and contrast the two approaches to array-oriented programming. Julia is another relatively new language, which focuses heavily on array oriented programming and type-based function overloading. Learning one of these languages is likely to provide insight into the capabilities of the Scientific Python stack, as well as providing opportunities to explore hardware level parallel execution through technologies like OpenCL and Nvidia's CUDA, and distributed data processing through ecosystems like Apache Spark and the Python-specific Blaze.

Statistical data analysis: R As access to large data sets has grown, so has demand for capable freely available analytical tools for processing those data sets. One such tool is the R programming language, which focuses specifically on statistical data analysis and visualisation. Learning R is likely to provide insight into the statistical analysis capabilities of the Scientific Python stack, especially the pandas data manipulation library and the seaborn statistical visualisation library.

Computational pipeline modelling: Haskell, Scala, Clojure, F# Object-oriented data modelling and array-oriented data processing focus a lot of attention on modelling data at rest, either in the form of collections of named attributes or as arrays of structured data. By contrast, functional programming languages emphasise the modelling of data in motion, in the form of computational flows. Learning at least the basics of functional programming can help greatly improve the structure of data transformation operations even in otherwise procedural, object-oriented or array-oriented applications. Haskell is a functional programming language that has had a significant influence on the design of Python, most notably through the introduction of list comprehensions in Python 2.0. Scala is an (arguably) functional programming language for the JVM that, together with Java, Python and R, is one of the four primary programming languages for the Apache Spark data analysis platform. While being designed to encourage functional programming approaches, Scala's syntax, data model, and execution model are also designed to minimise barriers to adoption for current Java programmers (hence the "arguably" - the case can be made that Scala is better categorised as an object-oriented programming language with strong functional programming support). Clojure is another functional programming language for the JVM that is designed as a dialect of Lisp. It earns its place in this list by being the inspiration for the toolz functional programming toolkit for Python. F# isn't a language I'm particularly familiar with myself, but seems worth noting as the preferred functional programming language for the .NET CLR. Learning one of these languages is likely to provide insight into Python's own computational pipeline modelling tools, including container comprehensions, generators, generator expressions, the functools and itertools standard library modules, and third party functional Python toolkits like toolz.

Event driven programming: JavaScript, Go, Erlang, Elixir Computational pipelines are an excellent way to handle data transformation and analysis problems, but many problems require that an application run as a persistent service that waits for events to occur, and then handles those events. In these kinds of services, it is usually essential to be able to handle multiple events concurrently in order to be able to accommodate multiple users (or at least multiple actions) at the same time. JavaScript was originally developed as an event handling language for web browsers, permitting website developers to respond locally to client side actions (such as mouse clicks and key presses) and events (such as the page rendering being completed). It is supported in all modern browsers, and together with the HTML5 Domain Object Model, has become a de facto standard for defining the appearance and behaviour of user interfaces. Go was designed by Google as a purpose built language for creating highly scalable web services, and has also proven to be a very capable language for developing command line applications. The most interesting aspect of Go from a programming language design perspective is its use of Communicating Sequential Processes concepts in its core concurrency model. Erlang was designed by Ericsson as a purpose built language for creating highly reliable telephony switches and similar devices, and is the language powering the popular RabbitMQ message broker. Erlang uses the Actor model as its core concurrency primitive, passing messages between threads of execution, rather than allowing them to share data directly. While I've never programmed in Erlang myself, my first full-time job involved working with (and on) an Actor-based concurrency framework for C++ developed by an ex-Ericsson engineer, as well as developing such a framework myself based on the TSK (Task) and MBX (Mailbox) primitives in Texas Instrument's lightweight DSP/BIOS runtime (now known as TI-RTOS). Elixir earns an entry on the list by being a language designed to run on the Erlang VM that exposes the same concurrency semantics as Erlang, while also providing a range of additional language level features to help provide a more well-rounded environment that is more likely to appeal to developers migrating from other languages like Python, Java, or Ruby. Learning one of these languages is likely to provide insight into Python's own concurrency and parallelism support, including native coroutines, generator based coroutines, the concurrent.futures and asyncio standard library modules, third party network service development frameworks like Twisted and Tornado, the channels concept being introduced to Django, and the event handling loops in GUI frameworks.

Gradual typing: TypeScript One of the more controversial features that landed in Python 3.5 was the new typing module, which brings a standard lexicon for gradual typing support to the Python ecosystem. For folks whose primary exposure to static typing is in languages like C, C++ and Java, this seems like an astoundingly terrible idea (hence the controversy). Microsoft's TypeScript, which provides gradual typing for JavaScript applications provides a better illustration of the concept. TypeScript code compiles to JavaScript code (which then doesn't include any runtime type checking), and TypeScript annotations for popular JavaScript libraries are maintained in the dedicated DefinitelyTyped repository. As Chris Neugebauer pointed out in his PyCon Australia presentation, this is very similar to the proposed relationship between Python, the typeshed type hint repository, and type inference and analysis tools like mypy. In essence, both TypeScript and type hinting in Python are ways of writing particular kinds of tests, either as separate files (just like normal tests), or inline with the main body of the code (just like type declarations in statically typed languages). In either case, you run a separate command to actually check that the rest of the code is consistent with the available type assertions (this occurs implicitly as part of the compilation to JavaScript for TypeScript, and as an entirely optional static analysis task for Python's type hinting).

Dynamic metaprogramming: Hy, Ruby A feature folks coming to Python from languages like C, C++, C# and Java often find disconcerting is the notion that "code is data": the fact that things like functions and classes are runtime objects that can be manipulated like any other object. Hy is a Lisp dialect that runs on both the CPython VM and the PyPy VM. Lisp dialects take the "code as data" concept to extremes, as Lisp code consists of nested lists describing the operations to be performed (the name of the language itself stands for "LISt Processor"). The great strength of Lisp-style languages is that they make it incredibly easy to write your own domain specific languages. The great weakness of Lisp-style languages is that they make it incredibly easy to write your own domain specific languages, which can sometimes make it difficult to read other people's code. Ruby is a language that is similar to Python in many respects, but as a community is far more open to making use of dynamic metaprogramming features that are "supported, but not encouraged" in Python. This includes things like reopening class definitions to add additional methods, and using closures to implement core language constructs like iteration. Learning one of these languages is likely to provide insight into Python's own dynamic metaprogramming support, including function and class decorators, monkeypatching, the unittest.mock standard library module, and third party object proxying modules like wrapt. (I'm not aware of any languages to learn that are likely to provide insight into Python's metaclass system, so if anyone has any suggestions on that front, please mention them in the comments. Metaclasses power features like the core type system, abstract base classes, enumeration types and runtime evaluation of gradual typing expressions)

Pragmatic problem solving: Lua, PHP, Perl Popular programming languages don't exist in isolation - they exist as part of larger ecosystems of redistributors (both commercial and community focused), end users, framework developers, tool developers, educators and more. Lua is a popular programming language for embedding in larger applications as a scripting engine. Significant examples include it being the language used to write add-ons for the World of Warcraft game client, and it's also embedded in the RPM utility used by many Linux distributions. Compared to CPython, a Lua runtime will generally be a tenth of the size, and its weaker introspection capabilities generally make it easier to isolate from the rest of the application and the host operating system. A notable contribution from the Lua community to the Python ecosystem is the adoption of the LuaJIT FFI (Foreign Function Interface) as the basis of the JIT-friendly cffi interface library for CPython and PyPy. PHP is another popular programming language that rose to prominence as the original "P" in the Linux-Apache-MySQL-PHP LAMP stack, due to its focus on producing HTML pages, and its broad availability on early Virtual Private Server hosting providers. For all the handwringing about conceptual flaws in various aspects of its design, it's now the basis of several widely popular open source web services, including the Drupal content management system, the Wordpress blogging engine, and the MediaWiki engine that powers Wikipedia. PHP also powers important services like the Ushahidi platform for crowdsourced community reporting on distributed events. Like PHP, Perl rose to popularity on the back of Linux. Unlike PHP, which grew specifically as a web development platform, Perl rose to prominence as a system administrator's tool, using regular expressions to string together and manipulate the output of text-based Linux operating system commands. When sh , awk and sed were no longer up to handling a task, Perl was there to take over. Learning one of these languages isn't likely to provide any great insight into aesthetically beautiful or conceptually elegant programming language design. What it is likely to do is to provide some insight into how programming language distribution and adoption works in practice, and how much that has to do with fortuitous opportunities, accidents of history and lowering barriers to adoption by working with redistributors to be made available by default, rather than the inherent capabilities of the languages themselves. In particular, it may provide insight into the significance of projects like CKAN, OpenStack NFV, Blender, SciPy, OpenMDAO, PyGMO, PyCUDA, the Raspberry Pi Foundation and Python's adoption by a wide range of commercial organisations, for securing ongoing institutional investment in the Python ecosystem.