Why is Python such a popular language in the AI field? First of all, I'm a beginner studying AI and this is not an opinion-oriented question or one to compare programming languages. I'm not implying that Python is the best language. But the fact is that most of the famous AI frameworks have primary support for Python. They can even be multilanguage supported, for example, TensorFlow that supports Python, C++, or CNTK from Microsoft that support C# and C++, but the most used is Python (I mean more documentation, examples, bigger community, support, etc). Even if you choose C# (developed by Microsoft and my primary programming language) you must have the Python environment set up.

I read in other forums that Python is preferred for AI because the code is simplified and cleaner, good for fast prototyping.

I was watching a movie with AI thematics (Ex_Machina). In some scenes, the main character hacks the interface of the house automation. Guess which language was on the scene? Python.

So what is the big deal with Python? 

Why is there a growing association between Python and AI?
Python comes with a huge amount of inbuilt libraries. Many of the libraries are for Artificial Intelligence and Machine Learning. Some of the libraries are TensorFlow (which is a high-level neural network library), scikit-learn (for data mining, data analysis and machine learning), pylearn2 (more flexible than scikit-learn), etc. The list keeps going and never ends. You can find some libraries here.
Python has an easy implementation for OpenCV. What makes Python favorite for everyone is its powerful and easy implementation.
For other languages, students and researchers need to get to know the language before getting into ML or AI with that language. This is not the case with Python. Even a programmer with very basic knowledge can easily handle Python. Apart from that, the time someone spends on writing and debugging code in Python is way less when compared to C, C++ or Java. This is exactly what the students of AI and ML want. They don't want to spend time on debugging the code for syntax errors, they want to spend more time on their algorithms and heuristics related to AI and ML
Not just the libraries but their tutorials, handling of interfaces are easily available online. People build their own libraries and upload them on GitHub or elsewhere to be used by others.
All these features make Python suitable for them.