Space Tracer

The Space Tracer displays what happens to your code so you can read through it like a book, instead of stepping through it like most debuggers. For example, here’s a simple script that assigns a variable, then loops a few times making changes to that variable, before printing out the final message.

message = 'Hello, World'
for i in range(3):
    message += '!'
print(message)

A regular debugger would let you set break points, look at variable values, and step through the code. Space Tracer shows you the code with all of the variable assignments, and the loop iterations in columns. Here, you see the script on the left, and the variable values and loops on the right, so you can read through what happened, like reading a book.

message = 'Hello, World' | message = 'Hello, World' 
for i in range(3):       | i = 0                     | i = 1                      | i = 2 
    message += '!'       | message = 'Hello, World!' | message = 'Hello, World!!' | message = 'Hello, World!!!' 
print(message)           | print('Hello, World!!!') 

You can run Space Tracer as a command-line tool, or you can use it in the Live Coding in Python plugins for PyCharm, Emacs, and Sublime Text. See the Getting Started page for a full introduction.

Installing Space Tracer

Space Tracer is a regular Python package, so you can install it with pip install space_tracer. If you haven’t installed Python packages before, read Brett Cannon’s quick-and-dirty guide.

Then copy the script above into a file called hello.py, and run it with the space_tracer command:

$ space_tracer hello.py
message = 'Hello, World' | message = 'Hello, World' 
for i in range(3):       | i = 0                     | i = 1                      | i = 2 
    message += '!'       | message = 'Hello, World!' | message = 'Hello, World!!' | message = 'Hello, World!!!' 
print(message)           | print('Hello, World!!!') 
$