Incorrect type annotations cause AttributeError on import

[pranavrajpal]

With the following code (using the Pillow library):

from PIL import Image

def test(im: Image):
    print(im.mode)

def run() -> None:
    im = Image.open('test.png')
    test(im)

and the following config file:

[mypy-PIL.*]
ignore_missing_imports = True

mypy shows no errors, but compiling the code with mypyc and trying to run it produces the following traceback:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "bug.py", line 1, in <module>
    from PIL import Image
AttributeError: module 'PIL' has no attribute 'Image'

The problem is that the type annotations in the original code are incorrect, because PIL.Image is a module, and PIL.Image.open is a function that returns a separate PIL.Image.Image object, so the correct type annotations are:

from PIL import Image
from PIL.Image import Image as ImageType

def test(im: ImageType):
    print(im.mode)

def run() -> None:
    im = Image.open('test.png')
    test(im)

which fixes the mypyc error.

---

There are a couple of possible solutions that I can think of to this:

1. Get mypy to realize the error in the original code, even when ignore_missing_imports is set, by noticing that a class is being passed in when a module is expected.
2. Same as (1), but only emit an error if compiling with mypyc.
3. Ignore any type annotations from untyped libraries when compiling with mypyc.
4. Insert code into the compiled C extension to check if this happens and print/raise with a nicer error message.

I'd like to work on this, but I don't really know which (if any) of the solutions I mentioned would be the best way to fix this.

[JelleZijlstra]

This looks like mypyc miscompiles from A import B as essentially import A; B = A.B.

Here's a snippet from the generated C code:

CPyL4: ;
    cpy_r_r8 = CPyStatic_unicode_1; /* 'PIL' */
    cpy_r_r9 = PyImport_Import(cpy_r_r8);
    if (unlikely(cpy_r_r9 == NULL)) {
        CPy_AddTraceback("pilly.py", "<module>", 1, CPyStatic_globals);
        goto CPyL9;
    } else
        goto CPyL5;
CPyL5: ;
    CPyModule_PIL = cpy_r_r9;
    CPy_INCREF(CPyModule_PIL);
    CPy_DecRef(cpy_r_r9);
    goto CPyL6;
CPyL6: ;
    cpy_r_r10 = CPyModule_PIL;
    cpy_r_r11 = CPyStatic_globals;
    cpy_r_r12 = CPyStatic_unicode_2; /* 'Image' */
    cpy_r_r13 = CPyObject_GetAttr(cpy_r_r10, cpy_r_r12);

The cpy_r_r9 line does essentially import PIL, and the cpy_r_r13 lines does getattr(PIL, "Image"). But that is wrong, because from A import B may end up importing A.B as a module.

This still reproduces if the module is just from PIL import Image, so it's not related to the incorrect type annotation in your code.

The solution would be to make the C code mypyc generates follow the runtime semantics of from ... import more closely.

[pranavrajpal]

What you're saying does make sense. I think the reason that the second python script happened to work correctly is because, looking at the generated C code:

CPyL4: ;
    cpy_r_r8 = CPyStatics[9]; /* 'PIL' */
    cpy_r_r9 = PyImport_Import(cpy_r_r8);
    if (unlikely(cpy_r_r9 == NULL)) {
        CPy_AddTraceback("fixed_bug.py", "<module>", 1, CPyStatic_globals);
        goto CPyL17;
    }
CPyL5: ;
    CPyModule_PIL = cpy_r_r9;
    CPy_INCREF(CPyModule_PIL);
    CPy_DecRef(cpy_r_r9);
CPyL6: ;
    cpy_r_r10 = CPyModule_PIL;
    cpy_r_r11 = CPyStatic_globals;
    cpy_r_r12 = CPyModule_PIL___Image;
    cpy_r_r13 = (PyObject *)&_Py_NoneStruct;
    cpy_r_r14 = cpy_r_r12 != cpy_r_r13;
    if (cpy_r_r14) goto CPyL9;
CPyL7: ;
    cpy_r_r15 = CPyStatics[10]; /* 'PIL.Image' */
    cpy_r_r16 = PyImport_Import(cpy_r_r15);
    if (unlikely(cpy_r_r16 == NULL)) {
        CPy_AddTraceback("fixed_bug.py", "<module>", 1, CPyStatic_globals);
        goto CPyL17;
    }
CPyL8: ;
    CPyModule_PIL___Image = cpy_r_r16;
    CPy_INCREF(CPyModule_PIL___Image);
    CPy_DecRef(cpy_r_r16);
CPyL9: ;
    cpy_r_r17 = CPyStatics[5]; /* 'Image' */
    cpy_r_r18 = CPyObject_GetAttr(cpy_r_r10, cpy_r_r17);
    if (unlikely(cpy_r_r18 == NULL)) {
        CPy_AddTraceback("fixed_bug.py", "<module>", 1, CPyStatic_globals);
        goto CPyL17;
    }

It appears to be doing the equivalent of:

import PIL
import PIL.Image
Image = getattr(PIL, "Image")

which happens to do the same thing as the original version by coincidence.

I'll take a look at this and see what I find.