Saying Python is popular in machine learning and artificial intelligence would not be wrong because Python has a lot of inbuilt libraries which deals with AI and ML. Many libraries are for high level nervous system. scikit-learn for data mining/warehousing, data examination and machine learning. pylearn2 is more suitable than scikit. There are a lot of libraries which is not possible to define here each of them separately. Considering about availability of libraries you can understand how flexible would be to start with Python in ML and AI. you can get reference about some libraries by visiting the URL:
People like Python because of its flexible and powerful implementation. It is very easy to develop a real time computer system in Python (OpenCV). A developer with basic knowledge can start with Python without putting much effort. In other languages, you need to know about the language properly then you can start but its not case with Python. You can develop a lot of functionality by writing very less code. Debugging in Python takes few moment as compared to Java, C and C++ that is what one needs while doing programming in AI and ML. Resources like tutorial and libraries can be easily found on Github etc. related to AI and ML. Not only libraries even interfaces are easily available online.
As per the above facts like availability, easy to program and getting developed in very less time and effort we can consider Python as a good platform/language of AI and ML.