mypy.semanal_pass1.SemanticAnalyzerPreAnalysis

Analyze reachability of blocks and imports and other local things.

This runs before semantic analysis, so names have not been bound. Imports are also not resolved yet, so we can only access the current module.

This determines static reachability of blocks and imports due to version and platform checks, among others.

The main entry point is 'visit_file'.

Reachability of imports needs to be determined very early in the build since this affects which modules will ultimately be processed.

Consider this example:

import sys

def do_stuff():

# type: () -> None: if sys.python_version < (3,):

import xyz # Only available in Python 2 xyz.whatever()

...

The block containing 'import xyz' is unreachable in Python 3 mode. The import shouldn't be processed in Python 3 mode, even if the module happens to exist.