Compile-time defines

bunpy build --define DEBUG=False --define VERSION=1.2.3 app.py

--define KEY=VALUE replaces occurrences of the bare name KEY in the compiled source with the literal VALUE before compilation. This is useful for:

• Feature flags (DEBUG, BETA, ENABLE_NEW_UI)
• Compile-time version strings
• Environment-specific configuration without runtime overhead

Example

# app.py
DEBUG = True   # will be replaced

if DEBUG:
    print("debug mode")

bunpy build --define DEBUG=False app.py

The compiled bytecode is equivalent to:

DEBUG = False

if DEBUG:   # constant fold → dead branch eliminated
    print("debug mode")

Limitations

• Only top-level bare name occurrences are replaced (not attribute access)
• VALUE is inserted as a Python literal; use quotes for strings: --define GREETING="'hello'" → GREETING = 'hello'
• Multiple --define flags can be combined