Optimize import mechanism#30
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There are two calls to mp_builtin___import__(): 1. ports/unix/main.c:main_() which provides a str in args[0] 2. py/runtime.c:mp_import_name() which provides a qstr in args[0] The default implementation of mp_builtin___import__() is mp_builtin___import___default() which has a different implementation based on MICROPY_ENABLE_EXTERNAL_IMPORT. If MICROPY_ENABLE_EXTERNAL_IMPORT is disabled then the handling of weak links assumes that args[0] is a `const char *`, when it is either a str or qstr object. Use the existing qstr of the module name instead, and also use a vstr instead of strcpy() to ensure no overflow occurs. (cherry picked from commit f8b0ae3)
This allows ports to override mp_builtin___import__. This can be useful in MicroPython applications where MICROPY_ENABLE_EXTERNAL_IMPORT has to be disabled due to its impact on build size (2% to 2.5% of the minimal port). By overriding the otherwise very minimal mp_builtin___import__, ports can still allow limited forms of application-specific imports. Signed-off-by: Laurens Valk <laurens@pybricks.com> (cherry picked from commit d8ad878)
If sys.path is enabled, but empty, this will now no longer search the filesystem. Previously an empty sys.path was equivalent to having `sys.path=[""]`. This is a breaking change, but this behavior now matches CPython. This also provides an alternative mechanism to the u-prefix to force an import of a builtin module: ``` import sys _path = sys.path[:] sys.path.clear() import foo # Forces the built-in foo. sys.path.extend(_path) del _path ``` Code size diff is -32 bytes on PYBV11. This work was funded through GitHub Sponsors. Signed-off-by: Jim Mussared <jim.mussared@gmail.com> (cherry picked from commit 42f3f66)
This makes it so that sub-packages are resolved relative to their parent's `__path__`, rather than re-resolving each parent's filesystem path. The previous behavior was that `import foo.bar` would first re-search `sys.path` for `foo`, then use the resulting path to find `bar`. For already-loaded and u-prefixed modules, because we no longer need to build the path from level to level, we no longer unnecessarily search the filesystem. This should improve startup time. Explicitly makes the resolving process clear: - Loaded modules are returned immediately without touching the filesystem. - Exact-match of builtins are also returned immediately. - Then the filesystem search happens. - If that fails, then the weak-link handling is applied. This maintains the existing behavior: if a user writes `import time` they will get time.py if it exits, otherwise the built-in utime. Whereas `import utime` will always return the built-in. This also fixes a regression from a7fa18c where we search the filesystem for built-ins. It is now only possible to override u-prefixed builtins. This will remove a lot of filesystem stats at startup, as micropython-specific modules (e.g. `pyb`) will no longer attempt to look at the filesystem. Added several improvements to the comments and some minor renaming and refactoring to make it clearer how the import mechanism works. Overall code size diff is +56 bytes on STM32. This work was funded through GitHub Sponsors. Signed-off-by: Jim Mussared <jim.mussared@gmail.com> (cherry picked from commit 5255577)
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mmilata
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Jun 16, 2026
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Upstream has lots of further changes in builtinimport.c but no commit seems to be a bugfix for anything introduced here so all good.
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Tested on all HW models -> trezor/trezor-firmware#7114 (comment) |
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Following trezor/trezor-firmware#7097.
The optimization is done in f5ec033 (micropython#11456, released in MicroPython 1.21), the first 3 commits are cherry-picked to avoid merge conflicts.