Static type checking with mypy

This does introduce some not-so-nice things, like having to annotate each
`__init__` function with `-> None`. However, the benefits of having static
type checking in a complex bit of software like BAT outweigh the downsides.

.gitignore

@@ -3,6 +3,7 @@
 __pycache__
 /*.egg-info/
 /.cache
+/.mypy_cache/
 /.pytest_cache
 .coverage
 /dist/

README.md

@@ -23,3 +23,11 @@ There are two object types used to represent file paths. Those are strictly sepa
 When it is necessary to interpret a `bpathlib.BlendPath` as a real path instead of a sequence of
 bytes, BAT first attempts to decode it as UTF-8. If that fails, the local filesystem encoding is
 used. The latter is also no guarantee of correctness, though.
+
+
+## Type checking
+
+The code statically type-checked with [mypy](http://mypy-lang.org/).
+
+Mypy likes to see the return type of `__init__` methods explicitly declared as `None`. Until issue
+[#604](https://github.com/python/mypy/issues/604) is resolved, we just do this in our code too.

blender_asset_tracer/blendfile/__init__.py

@@ -22,14 +22,13 @@
 
 import atexit
 import collections
+import functools
 import gzip
 import logging
 import os
 import struct
 import pathlib
 import tempfile
-
-import functools
 import typing
 
 from . import exceptions, dna_io, dna, header
@@ -40,8 +39,9 @@ log = logging.getLogger(__name__)
 FILE_BUFFER_SIZE = 1024 * 1024
 BLENDFILE_MAGIC = b'BLENDER'
 GZIP_MAGIC = b'\x1f\x8b'
+BFBList = typing.List['BlendFileBlock']
 
-_cached_bfiles = {}
+_cached_bfiles = {}  # type: typing.Dict[pathlib.Path, BlendFile]
 
 
 def open_cached(path: pathlib.Path, mode='rb', assert_cached=False) -> 'BlendFile':
@@ -94,7 +94,7 @@ class BlendFile:
     """
     log = log.getChild('BlendFile')
 
-    def __init__(self, path: pathlib.Path, mode='rb'):
+    def __init__(self, path: pathlib.Path, mode='rb') -> None:
         """Create a BlendFile instance for the blend file at the path.
 
         Opens the file for reading or writing pending on the access. Compressed
@@ -106,22 +106,21 @@ class BlendFile:
         self.filepath = path
         self.raw_filepath = path
         self._is_modified = False
+        self.fileobj = None  # type: typing.IO[bytes]
 
         self._open_file(path, mode)
 
-        self.blocks = []  # BlendFileBlocks, in disk order.
-        self.code_index = collections.defaultdict(list)
-        self.structs = []
-        self.sdna_index_from_id = {}
-        self.block_from_addr = {}
+        self.blocks = []  # type: BFBList
+        """BlendFileBlocks of this file, in disk order."""
 
-        try:
-            self.header = header.BlendFileHeader(self.fileobj, self.raw_filepath)
-            self.block_header_struct = self.header.create_block_header_struct()
-            self._load_blocks()
-        except Exception:
-            self.fileobj.close()
-            raise
+        self.code_index = collections.defaultdict(list)  # type: typing.Dict[bytes, BFBList]
+        self.structs = []  # type: typing.List[dna.Struct]
+        self.sdna_index_from_id = {}  # type: typing.Dict[bytes, int]
+        self.block_from_addr = {}  # type: typing.Dict[int, BlendFileBlock]
+
+        self.header = header.BlendFileHeader(self.fileobj, self.raw_filepath)
+        self.block_header_struct = self.header.create_block_header_struct()
+        self._load_blocks()
 
     def _open_file(self, path: pathlib.Path, mode: str):
         """Open a blend file, decompressing if necessary.
@@ -134,7 +133,10 @@ class BlendFile:
             correct magic bytes.
         """
 
-        fileobj = path.open(mode, buffering=FILE_BUFFER_SIZE)
+        if 'b' not in mode:
+            raise ValueError('Only binary modes are supported, not %r' % mode)
+
+        fileobj = path.open(mode, buffering=FILE_BUFFER_SIZE)  # typing.IO[bytes]
         fileobj.seek(0, os.SEEK_SET)
 
         magic = fileobj.read(len(BLENDFILE_MAGIC))
@@ -171,13 +173,16 @@ class BlendFile:
 
     def _load_blocks(self):
         """Read the blend file to load its DNA structure to memory."""
+
+        self.structs.clear()
+        self.sdna_index_from_id.clear()
         while True:
             block = BlendFileBlock(self)
             if block.code == b'ENDB':
                 break
 
             if block.code == b'DNA1':
-                self.structs, self.sdna_index_from_id = self.decode_structs(block)
+                self.decode_structs(block)
             else:
                 self.fileobj.seek(block.size, os.SEEK_CUR)
 
@@ -270,6 +275,10 @@ class BlendFile:
         DNACatalog is a catalog of all information in the DNA1 file-block
         """
         self.log.debug("building DNA catalog")
+
+        # Get some names in the local scope for faster access.
+        structs = self.structs
+        sdna_index_from_id = self.sdna_index_from_id
         endian = self.header.endian
         shortstruct = endian.USHORT
         shortstruct2 = endian.USHORT2
@@ -282,8 +291,6 @@ class BlendFile:
         data = self.fileobj.read(block.size)
         types = []
         typenames = []
-        structs = []
-        sdna_index_from_id = {}
 
         offset = 8
         names_len = intstruct.unpack_from(data, offset)[0]
@@ -346,8 +353,6 @@ class BlendFile:
                 dna_struct.append_field(field)
                 dna_offset += dna_size
 
-        return structs, sdna_index_from_id
-
     def abspath(self, relpath: bpathlib.BlendPath) -> bpathlib.BlendPath:
         """Construct an absolute path from a blendfile-relative path."""
 
@@ -391,7 +396,7 @@ class BlendFileBlock:
     old_structure = struct.Struct(b'4sI')
     """old blend files ENDB block structure"""
 
-    def __init__(self, bfile: BlendFile):
+    def __init__(self, bfile: BlendFile) -> None:
         self.bfile = bfile
 
         # Defaults; actual values are set by interpreting the block header.
@@ -406,7 +411,7 @@ class BlendFileBlock:
         Points to the data after the block header.
         """
         self.endian = bfile.header.endian
-        self._id_name = ...  # see the id_name property
+        self._id_name = ...  # type: typing.Union[None, ellipsis, bytes]
 
         header_struct = bfile.block_header_struct
         data = bfile.fileobj.read(header_struct.size)
@@ -448,7 +453,7 @@ class BlendFileBlock:
     def __hash__(self) -> int:
         return hash((self.code, self.addr_old, self.bfile.filepath))
 
-    def __eq__(self, other: 'BlendFileBlock') -> bool:
+    def __eq__(self, other: object) -> bool:
         if not isinstance(other, BlendFileBlock):
             return False
         return (self.code == other.code and
@@ -487,7 +492,10 @@ class BlendFileBlock:
                 self._id_name = self[b'id', b'name']
             except KeyError:
                 self._id_name = None
-        return self._id_name
+
+        # TODO(Sybren): figure out how to let mypy know self._id_name cannot
+        # be ellipsis at this point.
+        return self._id_name  # type: ignore
 
     def refine_type_from_index(self, sdna_index: int):
         """Change the DNA Struct associated with this block.
@@ -514,7 +522,7 @@ class BlendFileBlock:
         sdna_index = self.bfile.sdna_index_from_id[dna_type_id]
         self.refine_type_from_index(sdna_index)
 
-    def abs_offset(self, path: dna.FieldPath) -> (int, int):
+    def abs_offset(self, path: dna.FieldPath) -> typing.Tuple[int, int]:
         """Compute the absolute file offset of the field.
 
         :returns: tuple (offset in bytes, length of array in items)
@@ -563,18 +571,19 @@ class BlendFileBlock:
                            default=...,
                            null_terminated=True,
                            as_str=True,
-                           ) -> typing.Iterator[typing.Tuple[bytes, typing.Any]]:
+                           ) -> typing.Iterator[typing.Tuple[dna.FieldPath, typing.Any]]:
         """Generator, yields (path, property value) tuples.
 
         If a property cannot be decoded, a string representing its DNA type
         name is used as its value instead, between pointy brackets.
         """
+        path_full = path  # type: dna.FieldPath
         if path_root:
-            path_full = (
-                    (path_root if type(path_root) is tuple else (path_root,)) +
-                    (path if type(path) is tuple else (path,)))
-        else:
-            path_full = path
+            if isinstance(path_root, bytes):
+                path_root = (path_root,)
+            if isinstance(path, bytes):
+                path = (path,)
+            path_full = tuple(path_root) + tuple(path)
 
         try:
             # Try accessing as simple property
@@ -615,7 +624,7 @@ class BlendFileBlock:
             hsh = zlib.adler32(str(value).encode(), hsh)
         return hsh
 
-    def set(self, path: dna.FieldPath, value):
+    def set(self, path: bytes, value):
         dna_struct = self.bfile.structs[self.sdna_index]
         self.bfile.mark_modified()
         self.bfile.fileobj.seek(self.file_offset, os.SEEK_SET)

blender_asset_tracer/blendfile/dna.py

@@ -13,7 +13,7 @@ log = logging.getLogger(__name__)
 class Name:
     """dna.Name is a C-type name stored in the DNA as bytes."""
 
-    def __init__(self, name_full: bytes):
+    def __init__(self, name_full: bytes) -> None:
         self.name_full = name_full
         self.name_only = self.calc_name_only()
         self.is_pointer = self.calc_is_pointer()
@@ -72,7 +72,7 @@ class Field:
                  dna_type: 'Struct',
                  name: Name,
                  size: int,
-                 offset: int):
+                 offset: int) -> None:
         self.dna_type = dna_type
         self.name = name
         self.size = size
@@ -87,7 +87,7 @@ class Struct:
 
     log = log.getChild('Struct')
 
-    def __init__(self, dna_type_id: bytes, size: int = None):
+    def __init__(self, dna_type_id: bytes, size: int = None) -> None:
         """
         :param dna_type_id: name of the struct in C, like b'AlembicObjectPath'.
         :param size: only for unit tests; typically set after construction by
@@ -96,8 +96,8 @@ class Struct:
         """
         self.dna_type_id = dna_type_id
         self._size = size
-        self._fields = []
-        self._fields_by_name = {}
+        self._fields = []  # type: typing.List[Field]
+        self._fields_by_name = {}  # type: typing.Dict[bytes, Field]
 
     def __repr__(self):
         return '%s(%r)' % (type(self).__qualname__, self.dna_type_id)
@@ -183,7 +183,7 @@ class Struct:
 
     def field_get(self,
                   file_header: header.BlendFileHeader,
-                  fileobj: typing.BinaryIO,
+                  fileobj: typing.IO[bytes],
                   path: FieldPath,
                   default=...,
                   null_terminated=True,
@@ -263,7 +263,7 @@ class Struct:
 
     def field_set(self,
                   file_header: header.BlendFileHeader,
-                  fileobj: typing.BinaryIO,
+                  fileobj: typing.IO[bytes],
                   path: bytes,
                   value: typing.Any):
         """Write a value to the blend file.

blender_asset_tracer/blendfile/dna_io.py

@@ -16,7 +16,7 @@ class EndianIO:
     ULONG = struct.Struct(b'<Q')
 
     @classmethod
-    def _read(cls, fileobj: typing.BinaryIO, typestruct: struct.Struct):
+    def _read(cls, fileobj: typing.IO[bytes], typestruct: struct.Struct):
         data = fileobj.read(typestruct.size)
         try:
             return typestruct.unpack(data)[0]
@@ -24,35 +24,35 @@ class EndianIO:
             raise struct.error('%s (read %d bytes)' % (ex, len(data))) from None
 
     @classmethod
-    def read_char(cls, fileobj: typing.BinaryIO):
+    def read_char(cls, fileobj: typing.IO[bytes]):
         return cls._read(fileobj, cls.UCHAR)
 
     @classmethod
-    def read_ushort(cls, fileobj: typing.BinaryIO):
+    def read_ushort(cls, fileobj: typing.IO[bytes]):
         return cls._read(fileobj, cls.USHORT)
 
     @classmethod
-    def read_short(cls, fileobj: typing.BinaryIO):
+    def read_short(cls, fileobj: typing.IO[bytes]):
         return cls._read(fileobj, cls.SSHORT)
 
     @classmethod
-    def read_uint(cls, fileobj: typing.BinaryIO):
+    def read_uint(cls, fileobj: typing.IO[bytes]):
         return cls._read(fileobj, cls.UINT)
 
     @classmethod
-    def read_int(cls, fileobj: typing.BinaryIO):
+    def read_int(cls, fileobj: typing.IO[bytes]):
         return cls._read(fileobj, cls.SINT)
 
     @classmethod
-    def read_float(cls, fileobj: typing.BinaryIO):
+    def read_float(cls, fileobj: typing.IO[bytes]):
         return cls._read(fileobj, cls.FLOAT)
 
     @classmethod
-    def read_ulong(cls, fileobj: typing.BinaryIO):
+    def read_ulong(cls, fileobj: typing.IO[bytes]):
         return cls._read(fileobj, cls.ULONG)
 
     @classmethod
-    def read_pointer(cls, fileobj: typing.BinaryIO, pointer_size: int):
+    def read_pointer(cls, fileobj: typing.IO[bytes], pointer_size: int):
         """Read a pointer from a file."""
 
         if pointer_size == 4:
@@ -62,7 +62,7 @@ class EndianIO:
         raise ValueError('unsupported pointer size %d' % pointer_size)
 
     @classmethod
-    def write_string(cls, fileobj: typing.BinaryIO, astring: str, fieldlen: int) -> int:
+    def write_string(cls, fileobj: typing.IO[bytes], astring: str, fieldlen: int) -> int:
         """Write a (truncated) string as UTF-8.
 
         The string will always be written 0-terminated.
@@ -94,7 +94,7 @@ class EndianIO:
         return fileobj.write(encoded + b'\0')
 
     @classmethod
-    def write_bytes(cls, fileobj: typing.BinaryIO, data: bytes, fieldlen: int) -> int:
+    def write_bytes(cls, fileobj: typing.IO[bytes], data: bytes, fieldlen: int) -> int:
         """Write (truncated) bytes.
 
         When len(data) < fieldlen, a terminating b'\0' will be appended.

blender_asset_tracer/blendfile/exceptions.py

@@ -27,7 +27,7 @@ import pathlib
 class BlendFileError(Exception):
     """Raised when there was an error reading/parsing a blend file."""
 
-    def __init__(self, message: str, filepath: pathlib.Path):
+    def __init__(self, message: str, filepath: pathlib.Path) -> None:
         super().__init__(message)
         self.filepath = filepath
 
@@ -48,7 +48,7 @@ class NoReaderImplemented(NotImplementedError):
     :type dna_type: blender_asset_tracer.blendfile.dna.Struct
     """
 
-    def __init__(self, message: str, dna_name, dna_type):
+    def __init__(self, message: str, dna_name, dna_type) -> None:
         super().__init__(message)
         self.dna_name = dna_name
         self.dna_type = dna_type
@@ -61,7 +61,7 @@ class NoWriterImplemented(NotImplementedError):
     :type dna_type: blender_asset_tracer.blendfile.dna.Struct
     """
 
-    def __init__(self, message: str, dna_name, dna_type):
+    def __init__(self, message: str, dna_name, dna_type) -> None:
         super().__init__(message)
         self.dna_name = dna_name
         self.dna_type = dna_type
@@ -70,7 +70,7 @@ class NoWriterImplemented(NotImplementedError):
 class SegmentationFault(Exception):
     """Raised when a pointer to a non-existant datablock was dereferenced."""
 
-    def __init__(self, message: str, address: int, field_path=None):
+    def __init__(self, message: str, address: int, field_path=None) -> None:
         super().__init__(message)
         self.address = address
         self.field_path = field_path

blender_asset_tracer/blendfile/header.py

@@ -18,7 +18,7 @@ class BlendFileHeader:
     """
     structure = struct.Struct(b'7s1s1s3s')
 
-    def __init__(self, fileobj: typing.BinaryIO, path: pathlib.Path):
+    def __init__(self, fileobj: typing.IO[bytes], path: pathlib.Path) -> None:
         log.debug("reading blend-file-header %s", path)
         fileobj.seek(0, os.SEEK_SET)
         header = fileobj.read(self.structure.size)

blender_asset_tracer/blendfile/iterators.py

@@ -26,7 +26,7 @@ def sequencer_strips(sequence_editor: BlendFileBlock) \
     See blender_asset_tracer.cdefs.SEQ_TYPE_xxx for the type numbers.
     """
 
-    def iter_seqbase(seqbase) -> typing.Iterator[BlendFileBlock]:
+    def iter_seqbase(seqbase) -> typing.Iterator[typing.Tuple[BlendFileBlock, int]]:
         for seq in listbase(seqbase):
             seq.refine_type(b'Sequence')
             seq_type = seq[b'type']

blender_asset_tracer/cli/pack.py

@@ -2,6 +2,7 @@
 import logging
 import pathlib
 import sys
+import typing
 
 from blender_asset_tracer import pack
 
@@ -39,7 +40,7 @@ def cli_pack(args):
         raise SystemExit(1)
 
 
-def paths_from_cli(args) -> (pathlib.Path, pathlib.Path, pathlib.Path):
+def paths_from_cli(args) -> typing.Tuple[pathlib.Path, pathlib.Path, pathlib.Path]:
     """Return paths to blendfile, project, and pack target.
 
     Calls sys.exit() if anything is wrong.

blender_asset_tracer/pack/__init__.py

@@ -19,19 +19,23 @@ class PathAction(enum.Enum):
 
 
 class AssetAction:
-    def __init__(self):
+    """All the info required to rewrite blend files and copy assets."""
+
+    def __init__(self) -> None:
         self.path_action = PathAction.KEEP_PATH
-        self.usages = []
+        self.usages = []  # type: typing.List[result.BlockUsage]
         """BlockUsage objects referring to this asset.
 
         Those BlockUsage objects could refer to data blocks in this blend file
         (if the asset is a blend file) or in another blend file.
         """
 
-        self.new_path = None
+        self.new_path = None  # type: pathlib.Path
         """Absolute path to the asset in the BAT Pack."""
 
-        self.rewrites = []
+        self.read_from = None  # type: pathlib.Path
+
+        self.rewrites = []  # type: typing.List[result.BlockUsage]
         """BlockUsage objects in this asset that may require rewriting.
 
         Empty list if this AssetAction is not for a blend file.
@@ -43,7 +47,7 @@ class Packer:
                  blendfile: pathlib.Path,
                  project: pathlib.Path,
                  target: pathlib.Path,
-                 noop=False):
+                 noop=False) -> None:
         self.blendfile = blendfile
         self.project = project
         self.target = target
@@ -55,7 +59,8 @@ class Packer:
             log.warning('Running in no-op mode, only showing what will be done.')
 
         # Filled by strategise()
-        self._actions = collections.defaultdict(AssetAction)
+        self._actions = collections.defaultdict(
+            AssetAction)  # type: typing.DefaultDict[pathlib.Path, AssetAction]
 
         # Number of files we would copy, if not for --noop
         self._file_count = 0

blender_asset_tracer/pack/queued_copy.py

@@ -11,7 +11,7 @@ log = logging.getLogger(__name__)
 class FileCopyError(IOError):
     """Raised when one or more files could not be copied."""
 
-    def __init__(self, message, files_not_copied: typing.List[pathlib.Path]):
+    def __init__(self, message, files_not_copied: typing.List[pathlib.Path]) -> None:
         super().__init__(message)
         self.files_not_copied = files_not_copied
 
@@ -19,7 +19,7 @@ class FileCopyError(IOError):
 class FileCopier(threading.Thread):
     """Copies files in directory order."""
 
-    def __init__(self, *args, **kwargs):
+    def __init__(self, *args, **kwargs) -> None:
         super().__init__(*args, **kwargs)
 
         # For copying in a different process. By using a priority queue the files
@@ -31,7 +31,8 @@ class FileCopier(threading.Thread):
         # maxsize=100 is just a guess as to a reasonable upper limit. When this limit
         # is reached, the main thread will simply block while waiting for this thread
         # to finish copying a file.
-        self.file_copy_queue = queue.PriorityQueue(maxsize=100)
+        self.file_copy_queue = queue.PriorityQueue(
+            maxsize=100)  # type: queue.PriorityQueue[typing.Tuple[pathlib.Path, pathlib.Path]]
         self.file_copy_done = threading.Event()
 
     def queue(self, src: pathlib.Path, dst: pathlib.Path):

blender_asset_tracer/trace/blocks2assets.py

@@ -13,8 +13,8 @@ from . import result, modifier_walkers
 
 log = logging.getLogger(__name__)
 
-_warned_about_types = set()
-_funcs_for_code = {}
+_warned_about_types = set()  # type: typing.Set[bytes]
+_funcs_for_code = {}  # type: typing.Dict[bytes, typing.Callable]
 
 
 def iter_assets(block: blendfile.BlendFileBlock) -> typing.Iterator[result.BlockUsage]:

blender_asset_tracer/trace/expanders.py

@@ -11,7 +11,7 @@ from blender_asset_tracer.blendfile import iterators
 
 # Don't warn about these types at all.
 _warned_about_types = {b'LI', b'DATA'}
-_funcs_for_code = {}
+_funcs_for_code = {}  # type: typing.Dict[bytes, typing.Callable]
 log = logging.getLogger(__name__)
 
 

blender_asset_tracer/trace/file2blocks.py

@@ -7,12 +7,13 @@ blend files.
 """
 import collections
 import logging
+import pathlib
 import typing
 
 from blender_asset_tracer import blendfile, bpathlib
 from . import expanders
 
-_funcs_for_code = {}
+_funcs_for_code = {}  # type: typing.Dict[bytes, typing.Callable]
 log = logging.getLogger(__name__)
 
 
@@ -23,16 +24,16 @@ class _BlockIterator:
     without having to pass those variables to each recursive call.
     """
 
-    def __init__(self):
+    def __init__(self) -> None:
         # Set of (blend file Path, block address) of already-reported blocks.
-        self.blocks_yielded = set()
+        self.blocks_yielded = set()  # type: typing.Set[typing.Tuple[pathlib.Path, int]]
 
         # Queue of blocks to visit
-        self.to_visit = collections.deque()
+        self.to_visit = collections.deque()  # type: typing.Deque[blendfile.BlendFileBlock]
 
     def iter_blocks(self,
                     bfile: blendfile.BlendFile,
-                    limit_to: typing.Set[blendfile.BlendFileBlock] = frozenset(),
+                    limit_to: typing.Set[blendfile.BlendFileBlock] = set(),
                     ) -> typing.Iterator[blendfile.BlendFileBlock]:
         """Expand blocks with dependencies from other libraries."""
 

blender_asset_tracer/trace/file_sequence.py

@@ -8,7 +8,7 @@ log = logging.getLogger(__name__)
 class DoesNotExist(OSError):
     """Indicates a path does not exist on the filesystem."""
 
-    def __init__(self, path: pathlib.Path):
+    def __init__(self, path: pathlib.Path) -> None:
         super().__init__(path)
         self.path = path
 

blender_asset_tracer/trace/modifier_walkers.py

@@ -53,7 +53,8 @@ def _modifier_particle_system(modifier: blendfile.BlendFileBlock, block_name: by
 
     if flag & cdefs.PTCACHE_EXTERNAL:
         path, field = pointcache.get(b'path', return_field=True)
-        yield result.BlockUsage(pointcache, path, path_full_field=field,
+        bpath = bpathlib.BlendPath(path)
+        yield result.BlockUsage(pointcache, bpath, path_full_field=field,
                                 is_sequence=True, block_name=block_name)
 
 

blender_asset_tracer/trace/result.py

@@ -40,8 +40,8 @@ class BlockUsage:
                  path_full_field: dna.Field = None,
                  path_dir_field: dna.Field = None,
                  path_base_field: dna.Field = None,
-                 block_name: bytes = '',
-                 ):
+                 block_name: bytes = b'',
+                 ) -> None:
         if block_name:
             self.block_name = block_name
         else:
@@ -69,7 +69,9 @@ class BlockUsage:
         self.path_full_field = path_full_field
         self.path_dir_field = path_dir_field
         self.path_base_field = path_base_field
-        self._abspath = None  # cached by __fspath__()
+
+        # cached by __fspath__()
+        self._abspath = None  # type: pathlib.Path
 
     @staticmethod
     def guess_block_name(block: blendfile.BlendFileBlock) -> bytes:
@@ -134,7 +136,7 @@ class BlockUsage:
             raise NotImplemented()
         return self.block_name < other.block_name and self.block < other.block
 
-    def __eq__(self, other: 'BlockUsage'):
+    def __eq__(self, other: object):
         if not isinstance(other, BlockUsage):
             return False
         return self.block_name == other.block_name and self.block == other.block

setup.cfg

@@ -3,3 +3,9 @@ addopts = -v --cov blender_asset_tracer --cov-report term-missing
 
 [pep8]
 max-line-length = 100
+
+[mypy]
+# matches the latest Blender release
+python_version = 3.5
+
+warn_redundant_casts = True