You Might Not Want Async (in Python)

Asynchrony in Python had gathered much momentum recently, with interests from core developers, as evidenced by the introduction of `asyncio` in Python 3.4, and a great boom of related third-party projects following it. By utilising more functionalities from the underlying operating system, it is a great solution to many existing problems in Python applications, gaining practical concurrency without working around the well-known GIL (global interpreter lock) problem. With all its advantages, asynchrony is, however, still a relatively new concept in Python, and as a result could be somewhat mistaken, even misunderstood by some people. One of these misconceptions, probably the most serious, is to mistake concurrency through asynchrony for parallelism. Although `asyncio` (and other similar solutions) lets multiple parts of your program executes without interfering each other, it does *not* allow them to run together—this is still impossible, at least in CPython, due to the continued existence of the GIL. This makes asynchrony suitable for only a certain, instead of all, kinds of problems. Evaluation is therefore required before a programmer can decide whether the asynchrony model is suitable for a particular application. Furthermore, partly due to its relatively short existence, paradigms in asynchrony programming do not necessarily fit well with other parts of Python, including libraries, either built-in or third-party ones. Since only blocking libraries were available in most of Python’s history, many assumptions they made may not work well with async programs out-of-the-box. Adopting asynchrony, at least at the present time, will therefore introduce more technical debt to your program. These are all important aspects that require much consideration before you dive head-first into asynchrony.