CodeFlip and Python Tutor

Python Tutor made step-by-step visualization part of how programming is taught, and most teachers who find CodeFlip already know it. This page sets out where the two differ, including what CodeFlip doesn't do yet.

Checked in October 2026 against pythontutor.com, its list of unsupported features, and its last open-source release (2020). Details marked (2020) come from that release; the live site may have changed since.

At a glance

Where CodeFlip shows more

• A sentence for every step. "Line 3 ran: backup is now [90, 72, 85] (backup and scores both refer to this list)."
• C and C++ memory as it really is. Return values, memory leaks, dangling pointers, pointers just past the end of an array, unions, and C++ exceptions with the thrown object on the heap. Python Tutor documents C and C++ return values as not shown, and C++ features as largely untested.
• Standard containers as values. vector, map, string, smart pointers and weak_ptr are drawn as what they hold, not as library internals.
• Input in every language, including scanf, cin and Scanner, with the Input panel showing what has been read.
• Text files. Python, Java, C and C++ programs can read and write files you add beside the code; Python Tutor's programs can't open files.
• Newer language versions: Python 3.14 and Java 17 (records, switch expressions, text blocks), where Python Tutor's Java is Java 8 (2020).
• JavaScript's async code: Promises, async/await and timers, plus TypeScript.
• 2D arrays as grids, in every language, with a toggle to draw them as separate arrays.

Where they work the same way

• The layout: code on the left, frames and objects on the right, arrows between them.
• Steps follow lines, not parts of a line: f(g(x)) is one step.
• Neither runs GUI programs, network code, threads or command-line arguments.
• #break comments, clicked breakpoints, # pythontutor_hide: comments, keeping finished calls on screen, and live editing work in both.

What Python Tutor has that CodeFlip doesn't

• Teacher Mode: live coding with a class and in-class exercises. CodeFlip has no live shared sessions yet.
• Every JDK class. Python Tutor runs a real JVM; CodeFlip implements the parts of Java's library courses use, and anything else stops with a message naming the class.
• Some display options: drawing numbers and strings as objects, nesting objects inside each other, and text labels instead of arrows.

CodeFlip's known limitations

Every language

• Up to 10,000 steps per run, with limits on running time and on how deeply calls nest; past them, CodeFlip shows the steps so far and says why it stopped.
• No GUI, network, threads or command-line arguments.
• Files are text only, up to 64 KB each, with no folders of their own.
• LTI is launch only: grades aren't sent back to the LMS.

Python

• Python 3 only. Python 2 programs run as Python 3, so print x needs parentheses.

Java

• A teaching subset of the library: collections, streams, Optional, java.time dates and times, Scanner and file I/O. Time zones, Instant and other classes stop with a message naming them.
• Threads stop with a "can't run yet" message.

C and C++

• One source file per program: no programs split across .h and .cpp files yet.
• C++ programs need Chrome 137, Firefox 131 or Safari 18.4 or newer, because of how exceptions are compiled.

JavaScript and TypeScript

• No import/export, eval, new Function or Proxy. Async generators, for await and top-level await stop with a "can't run yet" message.
• TypeScript's types are removed before it runs, so type errors aren't reported, as with tsc --noCheck.

Switching

Python Tutor links and embeds open on CodeFlip when you change the domain. The migration guide converts them for you, and converts CodeFlip links back to Python Tutor if you ever want to return.

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