Python was conceived in the late 1980s as a successor to the ABC language. Python 2. 0, released 2000, introduced features like list comprehensions and a garbage collection system capable of collecting reference cycles. Python 3. 0, released 2008, was a major revision of the language that is not completely backward-compatible, and much Python 2 code does not run unmodified on Python 3. Due to concern about the amount of code written for Python 2, support for Python 2. 7 (the last release in the 2. x series) was extended to 2020. Language developer Guido van Rossum shouldered sole responsibility for the project until July 2018 but now shares his leadership as a member of a five-person steering council.