Port Spitfire to Python 3

[biplavbarua]

Port Spitfire to Python 3

Description

This PR ports the entire spitfire project to Python 3. It addresses syntax changes, standard library reorganization, unicode/bytes handling, and C extension APIs.

Changes

Vendored Libraries

• third_party/yapps2:
  • Converted print statements to functions.
  • Updated exception handling syntax (except E as v).
  • Removed deprecated string module functions and apply().
  • Replaced StringIO imports with io.

Core Spitfire

• Syntax:
  • Updated print(), exec(), raise.
  • Replaced basestring with str.
  • Replaced unicode() with str().
  • Updated dictionary iteration (iteritems -> items).
• Logic:
  • optimizer.py: Fixed iterator mutation bug by creating list copies of dictionary items during iteration.
  • util.py / codegen.py: Updated file opening modes to rb/wb to correctly handle binary data/encoding, ensuring strict bytes/str separation compliance.
  • Added missing import os in optimizer.py.

Scripts

• scripts/spitfire-compile: Updated for Python 3 I/O and exception handling.
• scripts/crunner.py:
  • Replaced cStringIO with io.
  • Added project root to sys.path.
  • Fixed output comparison logic (bytes vs str).

C Extensions

• _udn.c: Ported to Python 3 C API (module initialization, PyUnicode instead of PyString).
• _template.c: Ported to Python 3 C API.
• _baked.c: Disabled in setup.py. This extension relies deeply on Python 2 PyStringObject internals. The Python fallback (spitfire/runtime/baked.py) is fully functional and used instead.

Tests

• Templates: Updated tests/test-hoist-conditional-loop-optimization-3.txt to use $range() instead of $xrange().
• Expected Outputs: Updated test data in tests/output/ to match Python 3 exception messages and repr() output (e.g., removing u prefix).

Verification

Ran make test which executes unittest discovery and spitfire-compile integration tests.

• Result: All 124 tests passed.
• Optimization Levels: Verified at default, -O1, -O2, and -O3.
• Whitespace Mode: Verified --preserve-optional-whitespace tests.