Getting Started Developing

Just a couple of hints:

• You can parse a file and dump the parse tree by running mypy/parse.py as a script. This can make it easier to get familiar with the internals.

• A debugger can be a very useful way of getting familiar with a codebase. Specifically, if you try running mypy and get an unexpected error message, try searching for the corresponding string within messages.py. The messages.py file contains the bulk of the error-formatting and logging code.

  Attach a breakpoint to the corresponding line and run your debugger. Once it pauses, examine the stack trace: that should help give you an idea of how your input file was handled by mypy.

• Git blame can be a useful way of getting context into why a particular snippet of code exists. If you're not sure how to use git blame from the command line, you can use it from Github's web interface: navigate to a file and click the "blame" button in the upper-right.

• If you're repeatedly running mypy against several files and want to test or tweak something in the semantic analysis or type checking phase, consider disabling incremental mode via the --no-incremental flag. This will force mypy to re-check each file.