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Add by-design difference of object model

Paul Sokolovsky 2014-05-24 07:18:12 -07:00
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Differences.md

@ -5,6 +5,7 @@ MicroPython is intended for constrained environments, in particular, microcontro
1. MicroPython does not ship with an extensive standard library of modules. It's not possible and does not make sense, to provide the complete CPython3 library. Many modules are not usable or useful in the context of embedded systems, and there is not enough memory to deploy the entire library on small devices. So MicroPython takes the minimalist approach - only core datatypes (plus modules specific to particular hardware) are included with the interpreter, and all the rest is left as 3rd-party dependencies for particular user applications. The [micropython-lib](https://github.com/micropython/micropython-lib) project provides the non-monolithic standard library for MicroPython ([forum](http://forum.micropython.org/viewtopic.php?f=5&t=70)) 1. MicroPython does not ship with an extensive standard library of modules. It's not possible and does not make sense, to provide the complete CPython3 library. Many modules are not usable or useful in the context of embedded systems, and there is not enough memory to deploy the entire library on small devices. So MicroPython takes the minimalist approach - only core datatypes (plus modules specific to particular hardware) are included with the interpreter, and all the rest is left as 3rd-party dependencies for particular user applications. The [micropython-lib](https://github.com/micropython/micropython-lib) project provides the non-monolithic standard library for MicroPython ([forum](http://forum.micropython.org/viewtopic.php?f=5&t=70))
1. Unlike CPython3, which uses reference-counting, MicroPython uses garbage collection as the primary means of memory management. 1. Unlike CPython3, which uses reference-counting, MicroPython uses garbage collection as the primary means of memory management.
1. MicroPython does not implement complete CPython object data model, but only a subset of it. Advanced usages of multiple inheritance, ``__new__`` method may not work. Method resolution order is different (#525). Metaclasses are not supported (at least yet).
1. print() function does not check for recursive data structures, and if fed with such, may run in infinite loop. Note that if this is a concern to you, you can fix this at the Python application level. Do this by writing a function which keeps the history of each object visited, and override the builtin print() with your custom function. Such an implementation may of course use a lot of memory, which is why it's not implemented at the MicroPython level. 1. print() function does not check for recursive data structures, and if fed with such, may run in infinite loop. Note that if this is a concern to you, you can fix this at the Python application level. Do this by writing a function which keeps the history of each object visited, and override the builtin print() with your custom function. Such an implementation may of course use a lot of memory, which is why it's not implemented at the MicroPython level.
## Implementation Differences ## Implementation Differences