VISUALIZE Python, Java, JavaScript, TypeScript, Ruby, C, and C++ programs

Python Tutor, created by Philip Guo, helps people overcome a fundamental barrier to learning programming: understanding what happens as the computer executes each line of a program's source code.

Using this tool, you can write Python, Java, JavaScript, TypeScript, Ruby, C, and C++ programs in your Web browser and visualize what the computer is doing step-by-step as it executes those programs. So far, over 1.5 million people in over 180 countries have used Python Tutor to visualize over 15 million pieces of code, often as a supplement to textbooks, lecture notes, and online programming tutorials.

详见：http://pythontutor.com/