In 1986 I moved to a different project at CWI, the Amoeba project. Amoeba was a distributed operating system. By the late 1980s we found we needed a scripting language. I had a large degree of freedom on that project to start my own mini project within the scope of what we were doing. I remembered all my experience and some of my frustration with ABC. I decided to try to design a simple scripting language that possessed some of ABC's better properties, but without its problems.
So I started typing. I created a simple virtual machine, a simple parser, and a simple runtime. I made my own version of the various ABC parts that I liked. I created a basic syntax, used indentation for statement grouping instead of curly braces or begin-end blocks, and developed a small number of powerful data types: a hash table (or dictionary, as we call it), a list, strings, and numbers.
I took ABC's ingredients and shuffled them around a bit. Python was similar to ABC in many ways, but there were also differences. Python's lists, dictionaries, basic statements and use of indentation differed from what ABC had. ABC used uppercase for keywords. I never got comfortable with the uppercase, neither reading nor typing it, so in Python keywords were lowercase.
I think my most innovative contribution to Python's success was making it easy to extend. That also came out of my frustration with ABC. ABC was a very monolithic design. There was a language design team, and they were God. They designed every language detail and there was no way to add to it. You could write your own programs, but you couldn't easily add low-level stuff.