.. This document was generated by tools/gen-cpydiff.py

Builtin types
=============
Generated Wed 19 Jul 2023 21:24:18 UTC

Exception
---------

.. _cpydiff_types_exception_attrs:

All exceptions have readable ``value`` and ``errno`` attributes, not just ``StopIteration`` and ``OSError``.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Cause:** MicroPython is optimised to reduce code size.

**Workaround:** Only use ``value`` on ``StopIteration`` exceptions, and ``errno`` on ``OSError`` exceptions.  Do not use or rely on these attributes on other exceptions.

Sample code::

    e = Exception(1)
    print(e.value)
    print(e.errno)

+-----------------------------------------------------------------+---------------------------------------------------------------------+
| CPy output:                                                     | uPy output:                                                         |
+-----------------------------------------------------------------+---------------------------------------------------------------------+
| ::                                                              | ::                                                                  |
|                                                                 |                                                                     |
|     Traceback (most recent call last):                          |     /bin/sh: 1: ../ports/unix/build-standard/micropython: not found |
|       File "<stdin>", line 8, in <module>                       |                                                                     |
|     AttributeError: 'Exception' object has no attribute 'value' |                                                                     |
+-----------------------------------------------------------------+---------------------------------------------------------------------+

.. _cpydiff_types_exception_chaining:

Exception chaining not implemented
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sample code::

    try:
        raise TypeError
    except TypeError:
        raise ValueError

+-------------------------------------------------------------------------+---------------------------------------------------------------------+
| CPy output:                                                             | uPy output:                                                         |
+-------------------------------------------------------------------------+---------------------------------------------------------------------+
| ::                                                                      | ::                                                                  |
|                                                                         |                                                                     |
|     Traceback (most recent call last):                                  |     /bin/sh: 1: ../ports/unix/build-standard/micropython: not found |
|       File "<stdin>", line 8, in <module>                               |                                                                     |
|     TypeError                                                           |                                                                     |
|                                                                         |                                                                     |
|     During handling of the above exception, another exception occurred: |                                                                     |
|                                                                         |                                                                     |
|     Traceback (most recent call last):                                  |                                                                     |
|       File "<stdin>", line 10, in <module>                              |                                                                     |
|     ValueError                                                          |                                                                     |
+-------------------------------------------------------------------------+---------------------------------------------------------------------+

.. _cpydiff_types_exception_instancevar:

User-defined attributes for builtin exceptions are not supported
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Cause:** MicroPython is highly optimized for memory usage.

**Workaround:** Use user-defined exception subclasses.

Sample code::

    e = Exception()
    e.x = 0
    print(e.x)

+-------------+---------------------------------------------------------------------+
| CPy output: | uPy output:                                                         |
+-------------+---------------------------------------------------------------------+
| ::          | ::                                                                  |
|             |                                                                     |
|     0       |     /bin/sh: 1: ../ports/unix/build-standard/micropython: not found |
+-------------+---------------------------------------------------------------------+

.. _cpydiff_types_exception_loops:

Exception in while loop condition may have unexpected line number
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Cause:** Condition checks are optimized to happen at the end of loop body, and that line number is reported.

Sample code::

    l = ["-foo", "-bar"]
    
    i = 0
    while l[i][0] == "-":
        print("iter")
        i += 1

+--------------------------------------------+---------------------------------------------------------------------+
| CPy output:                                | uPy output:                                                         |
+--------------------------------------------+---------------------------------------------------------------------+
| ::                                         | ::                                                                  |
|                                            |                                                                     |
|     iter                                   |     /bin/sh: 1: ../ports/unix/build-standard/micropython: not found |
|     iter                                   |                                                                     |
|     Traceback (most recent call last):     |                                                                     |
|       File "<stdin>", line 10, in <module> |                                                                     |
|     IndexError: list index out of range    |                                                                     |
+--------------------------------------------+---------------------------------------------------------------------+

.. _cpydiff_types_exception_subclassinit:

Exception.__init__ method does not exist.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Cause:** Subclassing native classes is not fully supported in MicroPython.

**Workaround:** Call using ``super()`` instead::

    class A(Exception):
        def __init__(self):
            super().__init__()

Sample code::

    
    
    class A(Exception):
        def __init__(self):
            Exception.__init__(self)
    
    
    a = A()

+-------------+---------------------------------------------------------------------+
| CPy output: | uPy output:                                                         |
+-------------+---------------------------------------------------------------------+
|             | ::                                                                  |
|             |                                                                     |
|             |     /bin/sh: 1: ../ports/unix/build-standard/micropython: not found |
+-------------+---------------------------------------------------------------------+

bytearray
---------

.. _cpydiff_types_bytearray_sliceassign:

Array slice assignment with unsupported RHS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sample code::

    b = bytearray(4)
    b[0:1] = [1, 2]
    print(b)

+----------------------------------------+---------------------------------------------------------------------+
| CPy output:                            | uPy output:                                                         |
+----------------------------------------+---------------------------------------------------------------------+
| ::                                     | ::                                                                  |
|                                        |                                                                     |
|     bytearray(b'\x01\x02\x00\x00\x00') |     /bin/sh: 1: ../ports/unix/build-standard/micropython: not found |
+----------------------------------------+---------------------------------------------------------------------+

bytes
-----

.. _cpydiff_types_bytes_format:

bytes objects support .format() method
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Cause:** MicroPython strives to be a more regular implementation, so if both `str` and `bytes` support ``__mod__()`` (the % operator), it makes sense to support ``format()`` for both too. Support for ``__mod__`` can also be compiled out, which leaves only ``format()`` for bytes formatting.

**Workaround:** If you are interested in CPython compatibility, don't use ``.format()`` on bytes objects.

Sample code::

    print(b"{}".format(1))

+--------------------------------------------------------------+---------------------------------------------------------------------+
| CPy output:                                                  | uPy output:                                                         |
+--------------------------------------------------------------+---------------------------------------------------------------------+
| ::                                                           | ::                                                                  |
|                                                              |                                                                     |
|     Traceback (most recent call last):                       |     /bin/sh: 1: ../ports/unix/build-standard/micropython: not found |
|       File "<stdin>", line 7, in <module>                    |                                                                     |
|     AttributeError: 'bytes' object has no attribute 'format' |                                                                     |
+--------------------------------------------------------------+---------------------------------------------------------------------+

.. _cpydiff_types_bytes_keywords:

bytes() with keywords not implemented
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Workaround:** Pass the encoding as a positional parameter, e.g. ``print(bytes('abc', 'utf-8'))``

Sample code::

    print(bytes("abc", encoding="utf8"))

+-------------+---------------------------------------------------------------------+
| CPy output: | uPy output:                                                         |
+-------------+---------------------------------------------------------------------+
| ::          | ::                                                                  |
|             |                                                                     |
|     b'abc'  |     /bin/sh: 1: ../ports/unix/build-standard/micropython: not found |
+-------------+---------------------------------------------------------------------+

.. _cpydiff_types_bytes_subscrstep:

Bytes subscription with step != 1 not implemented
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Cause:** MicroPython is highly optimized for memory usage.

**Workaround:** Use explicit loop for this very rare operation.

Sample code::

    print(b"123"[0:3:2])

+-------------+---------------------------------------------------------------------+
| CPy output: | uPy output:                                                         |
+-------------+---------------------------------------------------------------------+
| ::          | ::                                                                  |
|             |                                                                     |
|     b'13'   |     /bin/sh: 1: ../ports/unix/build-standard/micropython: not found |
+-------------+---------------------------------------------------------------------+

dict
----

.. _cpydiff_types_dict_keys_set:

Dictionary keys view does not behave as a set.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Cause:** Not implemented.

**Workaround:** Explicitly convert keys to a set before using set operations.

Sample code::

    print({1: 2, 3: 4}.keys() & {1})

+-------------+---------------------------------------------------------------------+
| CPy output: | uPy output:                                                         |
+-------------+---------------------------------------------------------------------+
| ::          | ::                                                                  |
|             |                                                                     |
|     {1}     |     /bin/sh: 1: ../ports/unix/build-standard/micropython: not found |
+-------------+---------------------------------------------------------------------+

float
-----

.. _cpydiff_types_float_implicit_conversion:

uPy allows implicit conversion of objects in maths operations while CPython does not.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Workaround:** Objects should be wrapped in ``float(obj)`` for compatibility with CPython.

Sample code::

    
    
    class Test:
        def __float__(self):
            return 0.5
    
    
    print(2.0 * Test())

+----------------------------------------------------------------------+---------------------------------------------------------------------+
| CPy output:                                                          | uPy output:                                                         |
+----------------------------------------------------------------------+---------------------------------------------------------------------+
| ::                                                                   | ::                                                                  |
|                                                                      |                                                                     |
|     Traceback (most recent call last):                               |     /bin/sh: 1: ../ports/unix/build-standard/micropython: not found |
|       File "<stdin>", line 14, in <module>                           |                                                                     |
|     TypeError: unsupported operand type(s) for *: 'float' and 'Test' |                                                                     |
+----------------------------------------------------------------------+---------------------------------------------------------------------+

.. _cpydiff_types_float_rounding:

uPy and CPython outputs formats may differ
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sample code::

    print("%.1g" % -9.9)

+-------------+---------------------------------------------------------------------+
| CPy output: | uPy output:                                                         |
+-------------+---------------------------------------------------------------------+
| ::          | ::                                                                  |
|             |                                                                     |
|     -1e+01  |     /bin/sh: 1: ../ports/unix/build-standard/micropython: not found |
+-------------+---------------------------------------------------------------------+

int
---

.. _cpydiff_types_int_bit_length:

``bit_length`` method doesn't exist.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Cause:** bit_length method is not implemented.

**Workaround:** Avoid using this method on MicroPython.

Sample code::

    
    x = 255
    print("{} is {} bits long.".format(x, x.bit_length()))

+-------------------------+---------------------------------------------------------------------+
| CPy output:             | uPy output:                                                         |
+-------------------------+---------------------------------------------------------------------+
| ::                      | ::                                                                  |
|                         |                                                                     |
|     255 is 8 bits long. |     /bin/sh: 1: ../ports/unix/build-standard/micropython: not found |
+-------------------------+---------------------------------------------------------------------+

.. _cpydiff_types_int_subclassconv:

No int conversion for int-derived types available
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Workaround:** Avoid subclassing builtin types unless really needed. Prefer https://en.wikipedia.org/wiki/Composition_over_inheritance .

Sample code::

    
    
    class A(int):
        __add__ = lambda self, other: A(int(self) + other)
    
    
    a = A(42)
    print(a + a)

+-------------+---------------------------------------------------------------------+
| CPy output: | uPy output:                                                         |
+-------------+---------------------------------------------------------------------+
| ::          | ::                                                                  |
|             |                                                                     |
|     84      |     /bin/sh: 1: ../ports/unix/build-standard/micropython: not found |
+-------------+---------------------------------------------------------------------+

list
----

.. _cpydiff_types_list_delete_subscrstep:

List delete with step != 1 not implemented
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Workaround:** Use explicit loop for this rare operation.

Sample code::

    l = [1, 2, 3, 4]
    del l[0:4:2]
    print(l)

+-------------+---------------------------------------------------------------------+
| CPy output: | uPy output:                                                         |
+-------------+---------------------------------------------------------------------+
| ::          | ::                                                                  |
|             |                                                                     |
|     [2, 4]  |     /bin/sh: 1: ../ports/unix/build-standard/micropython: not found |
+-------------+---------------------------------------------------------------------+

.. _cpydiff_types_list_store_noniter:

List slice-store with non-iterable on RHS is not implemented
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Cause:** RHS is restricted to be a tuple or list

**Workaround:** Use ``list(<iter>)`` on RHS to convert the iterable to a list

Sample code::

    l = [10, 20]
    l[0:1] = range(4)
    print(l)

+----------------------+---------------------------------------------------------------------+
| CPy output:          | uPy output:                                                         |
+----------------------+---------------------------------------------------------------------+
| ::                   | ::                                                                  |
|                      |                                                                     |
|     [0, 1, 2, 3, 20] |     /bin/sh: 1: ../ports/unix/build-standard/micropython: not found |
+----------------------+---------------------------------------------------------------------+

.. _cpydiff_types_list_store_subscrstep:

List store with step != 1 not implemented
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Workaround:** Use explicit loop for this rare operation.

Sample code::

    l = [1, 2, 3, 4]
    l[0:4:2] = [5, 6]
    print(l)

+------------------+---------------------------------------------------------------------+
| CPy output:      | uPy output:                                                         |
+------------------+---------------------------------------------------------------------+
| ::               | ::                                                                  |
|                  |                                                                     |
|     [5, 2, 6, 4] |     /bin/sh: 1: ../ports/unix/build-standard/micropython: not found |
+------------------+---------------------------------------------------------------------+

str
---

.. _cpydiff_types_str_endswith:

Start/end indices such as str.endswith(s, start) not implemented
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sample code::

    print("abc".endswith("c", 1))

+-------------+---------------------------------------------------------------------+
| CPy output: | uPy output:                                                         |
+-------------+---------------------------------------------------------------------+
| ::          | ::                                                                  |
|             |                                                                     |
|     True    |     /bin/sh: 1: ../ports/unix/build-standard/micropython: not found |
+-------------+---------------------------------------------------------------------+

.. _cpydiff_types_str_formatsubscr:

Attributes/subscr not implemented
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sample code::

    print("{a[0]}".format(a=[1, 2]))

+-------------+---------------------------------------------------------------------+
| CPy output: | uPy output:                                                         |
+-------------+---------------------------------------------------------------------+
| ::          | ::                                                                  |
|             |                                                                     |
|     1       |     /bin/sh: 1: ../ports/unix/build-standard/micropython: not found |
+-------------+---------------------------------------------------------------------+

.. _cpydiff_types_str_keywords:

str(...) with keywords not implemented
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Workaround:** Input the encoding format directly. eg ``print(bytes('abc', 'utf-8'))``

Sample code::

    print(str(b"abc", encoding="utf8"))

+-------------+---------------------------------------------------------------------+
| CPy output: | uPy output:                                                         |
+-------------+---------------------------------------------------------------------+
| ::          | ::                                                                  |
|             |                                                                     |
|     abc     |     /bin/sh: 1: ../ports/unix/build-standard/micropython: not found |
+-------------+---------------------------------------------------------------------+

.. _cpydiff_types_str_ljust_rjust:

str.ljust() and str.rjust() not implemented
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Cause:** MicroPython is highly optimized for memory usage. Easy workarounds available.

**Workaround:** Instead of ``s.ljust(10)`` use ``"%-10s" % s``, instead of ``s.rjust(10)`` use ``"% 10s" % s``. Alternatively, ``"{:<10}".format(s)`` or ``"{:>10}".format(s)``.

Sample code::

    print("abc".ljust(10))

+-------------+---------------------------------------------------------------------+
| CPy output: | uPy output:                                                         |
+-------------+---------------------------------------------------------------------+
| ::          | ::                                                                  |
|             |                                                                     |
|     abc     |     /bin/sh: 1: ../ports/unix/build-standard/micropython: not found |
+-------------+---------------------------------------------------------------------+

.. _cpydiff_types_str_rsplitnone:

None as first argument for rsplit such as str.rsplit(None, n) not implemented
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sample code::

    print("a a a".rsplit(None, 1))

+------------------+---------------------------------------------------------------------+
| CPy output:      | uPy output:                                                         |
+------------------+---------------------------------------------------------------------+
| ::               | ::                                                                  |
|                  |                                                                     |
|     ['a a', 'a'] |     /bin/sh: 1: ../ports/unix/build-standard/micropython: not found |
+------------------+---------------------------------------------------------------------+

.. _cpydiff_types_str_subscrstep:

Subscript with step != 1 is not yet implemented
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sample code::

    print("abcdefghi"[0:9:2])

+-------------+---------------------------------------------------------------------+
| CPy output: | uPy output:                                                         |
+-------------+---------------------------------------------------------------------+
| ::          | ::                                                                  |
|             |                                                                     |
|     acegi   |     /bin/sh: 1: ../ports/unix/build-standard/micropython: not found |
+-------------+---------------------------------------------------------------------+

tuple
-----

.. _cpydiff_types_tuple_subscrstep:

Tuple load with step != 1 not implemented
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sample code::

    print((1, 2, 3, 4)[0:4:2])

+-------------+---------------------------------------------------------------------+
| CPy output: | uPy output:                                                         |
+-------------+---------------------------------------------------------------------+
| ::          | ::                                                                  |
|             |                                                                     |
|     (1, 3)  |     /bin/sh: 1: ../ports/unix/build-standard/micropython: not found |
+-------------+---------------------------------------------------------------------+

