Performance and limitations

Every function call is recorded, and every nontrivial expression is traced. This means that:

• Programs are greatly slowed down, and you should be wary of tracing functions that are called many times or that run through many loop iterations. Note that function calls are not visible in the interface until they have been completed.
• A large amount of data may be collected for every function call, especially for functions with many loop iterations and large nested objects and data structures. This may be a problem for memory both when running the program and viewing results in your browser.
• To limit the amount of data saved, only a sample is stored. Specifically:
  • The first and last 3 iterations of loops, except if an expression or statement is only evaluated at some point in the middle of a loop, in which case up to two iterations where it was evaluated will also be included (see Debugging the middle of a loop).
  • A limited version of the repr() of values is used, provided by the cheap_repr package.
  • Nested data structures and objects can only be expanded by up to 3 levels. Inside loops this is decreased, except when all current loops are in their first iteration.
  • Only pieces of objects are recorded - see Collecting more or less data.

In IPython shells and notebooks, shell.ast_transformers is ignored in decorated functions.