SlashData's survey reached over 19,000 respondents from 155 countries and offers a slightly different take on other language-popularity rankings from GitHub, RedMonk, Stack Overflow, and Tiobe.
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It estimates the second largest population of 10.1 million developers are Python users, while there are now 9.4 million Java developers.
The top three programming languages are the same as developer analyst firm RedMonk's rankings, which are based on data from GitHub and Stack Overflow.
SlashData estimates the next three largest developer communities are using C/C++ (7.3 million), Microsoft's C# (6.5 million), and PHP (6.3 million). Other large groups of developers are fans of Kotlin, Swift, Go, Ruby, Objective C, Rust and Lua.
Python is the fastest growing language with more than six million developers, according to SlashData, and 70% of developers focussed on machine learning (ML) report using it, likely due to ML libraries like Google-developed TensorFlow, Facebook's PyTorch, and NumPy. But Python is also widely used for backend systems automation.
"For perspective, only 17% use R, the other language often associated with data science," SlashData notes.
SlashData, however, notes that Rust and Lua were the two fastest growing programming language communities in the past 12 months, albeit from a lower base than Python.
Rust isn't widely used but this year its community stepped out of Mozilla's shadow and created its own Rust Foundation that's backed by Amazon Web Services, Microsoft Azure, Google and Mozilla.
Google is angling for Rust to become a second language for the Linux kernel and is using it to write new code for the Android operating system because of its memory safety guarantees that help avoid memory bugs. Developers also appreciate Rust's Crates package management system.