QUERY · ISSUE

Faulty exception: Implicit string conversion: bad_implicit_conversion(...)

openby Michael-dot-byteopened 2021-09-27updated 2026-03-24

proposed-close

Dear MicroPython community,

I stumbled upon a false exception when trying to implicitly convert a string to integer.
Error message should be: "can't convert 'str' object to int implicitly"
Rather than: "can't convert 'int' object to str implicitly" (see Traceback)

I'd be happy to see a fixture in future version or get any feedback of how to solve the issue.

Script:

def func(input1, input2):
return input1/input2

print(func(1,2))
print(func("1",2))

Result:

Traceback (most recent call last):
File "../implicit_conv_exception.py", line 7, in <module>
File "../implicit_conv_exception.py", line 4, in func
TypeError: can't convert 'int' object to str implicitly

Details:

Executed on Micropython v1.17
Port: unix
Methode causing error: STATIC NORETURN void bad_implicit_conversion(mp_obj_t self_in)

CANDIDATE · PULL REQUEST

py: Use correct exception message for implicit conversion to str or b…

closedby stinosopened 2017-03-14updated 2017-03-20

…ytes

When terse error reporting is not active use the actual target type in
the exception message instead of always reporting conversion 'to str'
fails even if it happens to actually be 'to bytes'. See #2957.

Note in the 3 functions near the end of the file I used 'str' as target type no matter what but that seems reasonable.

Also maybe it's worth having a check_implicit_conversion to reduce some duplication? Like

void check_bad_implicit_conversion(mp_obj_t src, mp_obj_type_t *targetType) {
    mp_obj_type_t *srcType = mp_obj_get_type(src);
    if (srcType  != targetType) {
        bad_implicit_conversion(srcType, targetType);
    }
}

so all occurrences of

if (mp_obj_get_type(args[1]) != self_type) {
    bad_implicit_conversion(args[1], self_type);
}

can be replaced with just check_bad_implicit_conversion(args[1], self_type)