Module mutation 

Mutation detection with escape analysis for Python — the fxrank-lang-python analog of fxrank-lang-ts’s detect/mutation.rs.

Python’s mutation story is simpler than Rust’s (no &mut / ownership) but more nuanced than JS’s: global and nonlocal declarations are function-wide (not position-dependent), and self.attr = … inside __init__ is construction (contained), not escaping state mutation.

Escape classification table

write site	kind	class	contained
global x declared, then x = … or x += …	global.mutation	6	false
nonlocal x declared, then x = … or x += …	this.mutation	3	false
self.attr = … in __init__	local.mutation	1	true
self.attr = … in a non-__init__ method	this.mutation	3	false
self.x.append(…) / self[i] = … (any method, incl. __init__)	this.mutation	3	false
write where root is a param name	param.mutation	3	false
write where root is a local binding	local.mutation	1	true

Strategy

1. Pre-scan the function body for global/nonlocal declarations and bare-Name LHS assignments — these build the globals, nonlocals, and locals sets.
2. Extract parameter names from unit.params.
3. Walk the body classifying write targets: Assign/AnnAssign/AugAssign targets, and mutating method calls (.append, .update, .add) via on_call in the EffectSink.

The contained bool returned alongside each Effect is the boundary-containment signal that Task 9’s discount consumes.

Functions

detect

Detect mutation effects in unit’s own body, with escape analysis.