Builtin Types

Generated Sun 21 Oct 2018 00:09:07 UTC

Exception

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 15, in <module>
  File "<stdin>", line 13, 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 paramter, 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 yet 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

float

uPy and CPython outputs formats may differ

Sample code:

print('%.1g' % -9.9)
CPy output: uPy output:
-1e+01
-10

int

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 11, in <module>
  File "<stdin>", line 8, in <lambda>
TypeError: can't convert A to 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 yet

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 yet 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)

Instance of a subclass of str cannot be compared for equality with an instance of a str

Sample code:

class S(str):
    pass

s = S('hello')
print(s == 'hello')
CPy output: uPy output:
True
False

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