Many comments have commented on the ecosystem, but I've thought a big reason behind python's success is that it's also a well designed language in terms of readability and lack of surprise. My background was in perl and shell scripting before finding python and the absolute beautiful form of the language (that whitespace is significant in more ways than one!) and its utter insistence that There's One And Only One Obvious Way To Do It (more or less) made programming much more ergonomic compared to the other similar scripting languages at the time.