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Python Tutor is a free web-based tool that helps students visualize code execution step by step. It supports multiple programming languages including Python, Java, C, C++, and JavaScript. As a teacher, I've found it invaluable for demonstrating programming concepts visually.

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Python Tutor helps you do programming homework assignments in Python, Java, C, C++, and JavaScript. It contains a unique step-by-step visual debugger and AI tutor to help you understand and debug code.

Since 2010, over 15 million people in more than 180 countries have used Python Tutor to visualize over 200 million pieces of code. It is the most widely-used program visualization tool for CS education.

As a preview, here is a small example showing recursion in Python:

Here are some examples of how it visualizes Java, C, and C++ code:

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Online Python Tutor - visualize, debug, get AI help for Python, Java, C, C++, and JavaScript

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Python Tutor helps you do programming homework assignments in Python, Java, C, C++, and JavaScript. It contains a unique step-by-step visual debugger and AI tutor to help you understand and debug code. Since 2010, over 15 million people in more than 180 countries have used Python Tutor to visualize over 200 million pieces of code.

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One of the best features of Python Tutor is that it's completely FREE! There's no premium version or hidden costs. This makes it accessible for all students regardless of their economic background, perfect for public school settings.

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The core feature is the ability to visualize code execution one step at a time. Students can see variables being created, values changing, and function calls in action. This is particularly helpful for understanding concepts like variable scope and recursion.

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Visualizing your Python code with "Python Tutor"

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While initially designed for Python, the tool now supports multiple programming languages. This makes it versatile for different CS courses and allows students to see how similar concepts work across different languages.

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Teachers can create permanent URLs for specific code examples, making it easy to share with students. There's also a live help mode where multiple users can view and discuss the same code visualization simultaneously.

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Python Tutor is ideal for beginners to intermediate programmers. I've successfully used it with both my beginning computer science course (language python) and in my upper level Advance Placement Computer Science course (language Java) with high school students. It's particularly effective for visual learners who struggle with abstract programming concepts.

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I use Python Tutor during live demonstrations, for homework assignments, and as a debugging tool. Students can submit links to their Python Tutor visualizations, allowing me to see exactly where they're struggling.

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Python Tutor excellently applies the multimedia principle by combining visual representations (memory diagrams) with verbal explanations. This dual-coding approach helps students form stronger mental models of programming concepts.

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The step-by-step visualization helps manage cognitive load by breaking down complex processes into manageable chunks. This prevents overwhelming students with too much information at once.

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This link will guide you step by step through examples of how to use pythontutor.com with your students learning Java.

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Summary: This article is meant for instructors who teach Java programming. Despite its name, Python Tutor is a widely-used web-based visualizer for Java that helps students to understand and debug their code. It visualizes the majority of object-oriented programming concepts taught in introductory college courses (e.g., CS1 and CS2), high school AP Computer Science, and intermediate-level Java programming. The Java visualizer will always remain free to use.

Python Tutor is a free tool that has been used by tens of millions of people since 2010 to visualize and debug code step-by-step. Despite its name, it also visualizes Java code ( in addition to C, C++, and JavaScript) to help students understand critical concepts and debug homework assignments.

These Java visualizations are well-aligned with the curricula of university-level introductory programming courses (e.g., CS1 and CS2), high school AP Computer Science A, and object-oriented programming courses taught in Java.

This article shows instructors how Python Tutor can automatically illustrate key concepts from a wide range of Java-based courses. If you think this tool may be helpful for your staff or students, please share this direct link in relevant course materials, chat groups, mailing lists, discussion forums, or social media:

(Also, if you teach in C or C++, check out what the C/C++ visualizer can do as well.)

Credits: The original Java visualizer was created in 2013 by David Pritchard and Will Gwozdz. It has since been enhanced in various ways over the years. Most notably, in 2023 the server infrastructure was upgraded so it now runs faster and more reliably.

The Java visualizer can illustrate most object-oriented programming concepts that are taught in introductory and intermediate-level classes (no pun intended), including:

constructor and super() calls

method calls

the this reference

static methods and fields

inheritance

polymorphism

method overloading vs. overriding

composition vs. inheritance

object-oriented design patterns

inner classes, anonymous classes, lambdas

The tool generates visual representations of classes, objects, methods, and fields (a.k.a. attributes), helping students to grasp the relationships and interactions among these elements. Students can observe the instantiation of objects, the calling of methods, and the changing states of object fields, thus making these abstract concepts more concrete.

Here's an example showing inheritance, which I derived (no pun intended) from code in the CSAwesome e-textbook:

This program instantiates three instances of the Student class, assigns them to local variables within main(), and adds them to the arrayOfPeople array. The array contains references (arrows) pointing to each instance.

Step through execution using the slider below the code to see each Student construtor being called, which in turn uses super() to call the Person superclass's constructor. Note how the static field Student.nextId increments after each constructor call.

Here's an example of polymorphism using dogs and cats as subclasses of Animal:

In the current step (Step 24), the stack contains main(), which calls System.out.println, which in turn calls the toString() method of the Cat instance, which calls the getName() method of its superclass, which returns"Whiskers". Note how the this reference for all the methods refers to the Cat instance.

Step back and forth using the slider to see polymorphism in action - either the Dog or Cat toString() method is called based on the run-time type of each Animal instance in the for loop.

It can be hard for beginners to understand how parameters of various types are passed to Java method calls. Step-by-step visualizations can help clarify:

In this example, here at Step 9 the swapCarYears() method is being called with the toyota and ford objects as parameters. The visualization shows how references to these objects are passed into the method as c1 and c2, respectively. The objects themselves are not copied (unlike in, say, C++) ... the references to them are.

In contrast, step forward to Step 14 when updateNumCars() gets called. Here the current value of numCars is passed into the method as myNumCars (effectively running myNumCars = numCars). So incrementing myNumCars++ within that method does not alter the original numCars.

You may have noticed from the prior example that string values are displayed inline within the two Car instances. Here are those same object instances again, with an added desc local variable that's also a string:

This inline visualization matches how we intuitively think about strings, but strings in Java are actually objects just like Car. So that means it's technically more accurate to draw them standalone with references (arrows) pointing to them, like this:

Note how each String object is now standalone. Users can activate this display mode by selecting "render all objects on the heap" below the code editor:

However, it's not on by default since visualizations tend to look too cluttered when this mode is on due to too many objects and arrows appearing on-screen.

Similarly, when this mode is on, wrapped objects (e.g., instances of Boolean, Integer, or Float) display standalone with references pointing to them, unlike primitives such as bool, int, and float, which appear inline within the stack frame:

We've already seen one-dimensional arrays in some of the above examples. Here's a multi-dimensional array, which is represented in Java as an array of arrays:

[Future work: implementing similar visualizations for ArrayList, LinkedList, and other Java Collections classes]

Stack frame visualizations are also useful for demonstrating recursion. Here is the classic factorial example:

You can also visualize more complex recursion, such as these examples in the CSAwesome e-textbook. Here is their binary search example:

Visualizations can also help students understand unusual control flow during exception handling. This is especially useful when exceptions occur across different method calls and when there are try, catch, and finally blocks. Here's a small example:

The Java visualizer in Python Tutor can help your students understand and debug a variety of code that they encounter in introductory or intermediate-level courses.

Feel free to share this direct link in relevant course materials, chat groups, mailing lists, discussion forums, social media, or anywhere else:

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How the Python Tutor visualizer can help students in your Java programming courses - Python Tutor

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Summary: This article is meant for instructors who teach Java programming. Despite its name, Python Tutor is a widely-used web-based visualizer for Java that helps students to understand and debug their code. It visualizes the majority of object-oriented programming concepts taught in introductory college courses (e.g., CS1 and CS2), high school AP Computer Science, and intermediate-level Java programming. The Java visualizer will always remain free to use.

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You can follow pythontutor.com on different platforms. This is a link to their instagram account.

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Welcome back to Instagram. Sign in to check out what your friends, family & interests have been capturing & sharing around the world.

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A key principle in computer science is tracing. We define tracing as the step by step process the computer takes as it reads through the code. Students need to learn track the variables and predict the outcome of the code. Understanding the steps the computer takes during compilation allows students to see errors and make corrections as needed.

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I use this site to demonstrate how the tool works as well as to teach how to trace the code. This is incredibly useful and saves time drawing it on the board.