Builtin types¶
Generated Wed 27 Dec 2023 12:47:14 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'
|
1
1
|
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
|
Traceback (most recent call last):
File "<stdin>", line 10, in <module>
ValueError:
|
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
|
Traceback (most recent call last):
File "<stdin>", line 8, in <module>
AttributeError: 'Exception' object has no attribute 'x'
|
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
|
iter
iter
Traceback (most recent call last):
File "<stdin>", line 12, in <module>
IndexError: list index out of range
|
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: |
Traceback (most recent call last):
File "<stdin>", line 18, in <module>
File "<stdin>", line 15, in __init__
AttributeError: type object 'Exception' has no attribute '__init__'
|
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')
|
Traceback (most recent call last):
File "<stdin>", line 8, in <module>
NotImplementedError: array/bytes required on right side
|
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'
|
b'1'
|
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'
|
Traceback (most recent call last):
File "<stdin>", line 7, in <module>
NotImplementedError: keyword argument(s) not implemented - use normal args instead
|
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'
|
Traceback (most recent call last):
File "<stdin>", line 7, in <module>
NotImplementedError: only slices with step=1 (aka None) are supported
|
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}
|
Traceback (most recent call last):
File "<stdin>", line 7, in <module>
TypeError: unsupported types for __and__: 'dict_view', 'set'
|
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'
|
1.0
|
uPy and CPython outputs formats may differ¶
Sample code:
print("%.1g" % -9.9)
CPy output: |
uPy output: |
-1e+01
|
-10
|
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.
|
Traceback (most recent call last):
File "<stdin>", line 9, in <module>
AttributeError: 'int' object has no attribute 'bit_length'
|
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
|
Traceback (most recent call last):
File "<stdin>", line 14, in <module>
File "<stdin>", line 10, in <lambda>
TypeError: unsupported types for __radd__: 'int', 'int'
|
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]
|
Traceback (most recent call last):
File "<stdin>", line 8, in <module>
NotImplementedError:
|
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]
|
Traceback (most recent call last):
File "<stdin>", line 8, in <module>
TypeError: object 'range' isn't a tuple or list
|
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]
|
Traceback (most recent call last):
File "<stdin>", line 8, in <module>
NotImplementedError:
|
str¶
Start/end indices such as str.endswith(s, start) not implemented¶
Sample code:
print("abc".endswith("c", 1))
CPy output: |
uPy output: |
True
|
Traceback (most recent call last):
File "<stdin>", line 7, in <module>
NotImplementedError: start/end indices
|
Attributes/subscr not implemented¶
Sample code:
print("{a[0]}".format(a=[1, 2]))
CPy output: |
uPy output: |
1
|
Traceback (most recent call last):
File "<stdin>", line 7, in <module>
NotImplementedError: attributes not supported
|
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
|
Traceback (most recent call last):
File "<stdin>", line 7, in <module>
NotImplementedError: keyword argument(s) not implemented - use normal args instead
|
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
|
Traceback (most recent call last):
File "<stdin>", line 7, in <module>
AttributeError: 'str' object has no attribute 'ljust'
|
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']
|
Traceback (most recent call last):
File "<stdin>", line 7, in <module>
NotImplementedError: rsplit(None,n)
|
Subscript with step != 1 is not yet implemented¶
Sample code:
print("abcdefghi"[0:9:2])
CPy output: |
uPy output: |
acegi
|
Traceback (most recent call last):
File "<stdin>", line 7, in <module>
NotImplementedError: only slices with step=1 (aka None) are supported
|
tuple¶
Tuple load with step != 1 not implemented¶
Sample code:
print((1, 2, 3, 4)[0:4:2])
CPy output: |
uPy output: |
(1, 3)
|
Traceback (most recent call last):
File "<stdin>", line 7, in <module>
NotImplementedError: only slices with step=1 (aka None) are supported
|