This will probably sound very negative, and while I think there's a need for a nice library to help bring to light what happens to data in your code, I don't think the pyscribe way of doing it (using sugar to transcribing a piece of code into one with more logging) is very useful in the long run.
For one, it seems the only type of change you can watch for are changes via assignment for top level variables. For example, any of the mutable built-ins (and I confirmed this by trying to use pyscribe) can't be watched for all changes. For example, mutating the list later with .append() doesn't log anything, nor does changing a value in a dictionary. You also can't watch a particular key in a dictionary, or an attribute in a class (these lead to parse errors when trying to run pyscribe).
Even if you modified the code to support this, you wouldn't be able to control access everywhere that piece of data went. Suppose I had a dict and and some point:
...
d = {'foo': 'bar'}
ps.watch(d)
ThirdPartyLib.do_stuff(d)
If that third party library mutated d, there'd be no way for you to know, unless you also were able to desugar those files (basically impossible because in some cases the source code isn't even available).
In any case, this type of mutation is generally what causes the most bugs. A value changing by assignment doesn't need a run-time logger. These change are in plain sight; just do a search for the variable name in the local body of the function. Mutation that occurs in other contexts (when the object has been renamed, or passed to another function where access is through a different variable name) is the difficult thing to debug, and pyscribe cannot handle that with the current design.
Honestly, I think this is better handled with mocking objects. See how python Mock library does things, and possibly use it yourself (it wouldn't be all that much work to write your own wrapper, but Mock is seriously powerful). Basically watching a variable means wrapping it with a mocked object that defers all reads/writes to the real object, while logging all those changes. Not relying on desugaring also means you can watch what happens to your data when you pass it into third party libraries.
Negative or not, I really appreciate the constructive criticism.
In response to your comments on watch: Indeed, right now it only identifies AST nodes of type "asgn". I imagine other mutations like append and others have different types too, I just haven't gotten around to implementing that. My bad for posting this in a pre-release state.
"Even if you modified the code to support this, you wouldn't be able to control access everywhere that piece of data went."
I can see two potential solutions:
1. Identifying nodes of type "call" that have a watched variable as an arg, and then adding an if statement to check if it has changed and printing it only if it has.
2. Analyzing AST of ThirdPartyLib.do_stuff(arg1), identify statements that mutate arg1, and logging a change after the call in the original program if arg1 is changed. This way even if the value isn't changed, it's still logged because it was mutated (or at least attempted to), which is probably more desirable than solution 1.
In response to Mock: Aside from Mock, people have told me they prefer the logging library, pdb, IDEs, etc. for debugging. PyScribe isn't meant to be a separate method of debugging, I intended it to supplement my preferred way, which is just using print statements. Might be it's not the most powerful, but its purpose isn't to compete with other methods of debugging.
For one, it seems the only type of change you can watch for are changes via assignment for top level variables. For example, any of the mutable built-ins (and I confirmed this by trying to use pyscribe) can't be watched for all changes. For example, mutating the list later with .append() doesn't log anything, nor does changing a value in a dictionary. You also can't watch a particular key in a dictionary, or an attribute in a class (these lead to parse errors when trying to run pyscribe).
Even if you modified the code to support this, you wouldn't be able to control access everywhere that piece of data went. Suppose I had a dict and and some point:
If that third party library mutated d, there'd be no way for you to know, unless you also were able to desugar those files (basically impossible because in some cases the source code isn't even available).In any case, this type of mutation is generally what causes the most bugs. A value changing by assignment doesn't need a run-time logger. These change are in plain sight; just do a search for the variable name in the local body of the function. Mutation that occurs in other contexts (when the object has been renamed, or passed to another function where access is through a different variable name) is the difficult thing to debug, and pyscribe cannot handle that with the current design.
Honestly, I think this is better handled with mocking objects. See how python Mock library does things, and possibly use it yourself (it wouldn't be all that much work to write your own wrapper, but Mock is seriously powerful). Basically watching a variable means wrapping it with a mocked object that defers all reads/writes to the real object, while logging all those changes. Not relying on desugaring also means you can watch what happens to your data when you pass it into third party libraries.