Builtin types¶

Generated Tue 23 Jul 2024 04:50:56 UTC

Exception¶

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): File "<stdin>", line 8, in <module> AttributeError: 'Exception' object has no attribute 'value'	/bin/sh: 1: ../ports/unix/build-standard/micropython: not found

Exception chaining not implemented¶

Sample code:

try:
    raise TypeError
except TypeError:
    raise ValueError

CPy output:

uPy output:

Traceback (most recent call last):
  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

/bin/sh: 1: ../ports/unix/build-standard/micropython: not found

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

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

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¶

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¶

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): File "<stdin>", line 7, in <module> AttributeError: 'bytes' object has no attribute 'format'	/bin/sh: 1: ../ports/unix/build-standard/micropython: not found

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

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¶

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¶

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): File "<stdin>", line 14, in <module> TypeError: unsupported operand type(s) for *: 'float' and 'Test'	/bin/sh: 1: ../ports/unix/build-standard/micropython: not found

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¶

`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

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¶

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

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

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

memoryview¶

memoryview can become invalid if its target is resized¶

Cause: CPython prevents a bytearray or io.bytesIO object from changing size while there is a memoryview object that references it. MicroPython requires the programmer to manually ensure that an object is not resized while any memoryview references it.

In the worst case scenario, resizing an object which is the target of a memoryview can cause the memoryview(s) to reference invalid freed memory (a use-after-free bug) and corrupt the MicroPython runtime.

Workaround: Do not change the size of any bytearray or io.bytesIO object that has a memoryview assigned to it.

Sample code:

b = bytearray(b"abcdefg")
m = memoryview(b)
b.extend(b"hijklmnop")
print(b, bytes(m))

CPy output:	uPy output:
Traceback (most recent call last): File "<stdin>", line 11, in <module> BufferError: Existing exports of data: object cannot be re-sized	/bin/sh: 1: ../ports/unix/build-standard/micropython: not found

str¶

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

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

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

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

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

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¶

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

Builtin types¶

Exception¶

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

Exception chaining not implemented¶

User-defined attributes for builtin exceptions are not supported¶

Exception in while loop condition may have unexpected line number¶

Exception.__init__ method does not exist.¶

bytearray¶

Array slice assignment with unsupported RHS¶

bytes¶

bytes objects support .format() method¶

bytes() with keywords not implemented¶

Bytes subscription with step != 1 not implemented¶

dict¶

Dictionary keys view does not behave as a set.¶

float¶

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

uPy and CPython outputs formats may differ¶

int¶

bit_length method doesn’t exist.¶

No int conversion for int-derived types available¶

list¶

List delete with step != 1 not implemented¶

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

List store with step != 1 not implemented¶

memoryview¶

memoryview can become invalid if its target is resized¶

str¶

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

Attributes/subscr not implemented¶

str(…) with keywords not implemented¶

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

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

Subscript with step != 1 is not yet implemented¶

tuple¶

Tuple load with step != 1 not implemented¶

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

Exception.init method does not exist.¶

`bit_length` method doesn’t exist.¶