Merge pull request #24773 from tailsu:sd/pathlike

python: accept path-like objects wherever file names are expected #24773

Merry Christmas, all 🎄

Implements #15731

Support is enabled for all arguments named `filename` or `filepath` (case-insensitive), or annotated with `CV_WRAP_FILE_PATH`.

Support is based on `PyOS_FSPath`, which is available in Python 3.6+. When running on older Python versions the arguments must have a `str` value as before.

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake

modules/python/src2/cv2.hpp

@@ -45,17 +45,20 @@ class ArgInfo
 private:
     static const uint32_t arg_outputarg_flag     = 0x1;
     static const uint32_t arg_arithm_op_src_flag = 0x2;
+    static const uint32_t arg_pathlike_flag      = 0x4;
 
 public:
     const char* name;
     bool outputarg;
     bool arithm_op_src;
+    bool pathlike;
     // more fields may be added if necessary
 
     ArgInfo(const char* name_, uint32_t arg_) :
         name(name_),
         outputarg((arg_ & arg_outputarg_flag) != 0),
-        arithm_op_src((arg_ & arg_arithm_op_src_flag) != 0) {}
+        arithm_op_src((arg_ & arg_arithm_op_src_flag) != 0),
+        pathlike((arg_ & arg_pathlike_flag) != 0) {}
 
 private:
     ArgInfo(const ArgInfo&) = delete;

modules/python/src2/cv2_convert.cpp

@@ -701,6 +701,18 @@ bool pyopencv_to(PyObject* obj, String &value, const ArgInfo& info)
         return true;
     }
     std::string str;
+
+#if ((PY_VERSION_HEX >= 0x03060000) && !defined(Py_LIMITED_API)) || (Py_LIMITED_API >= 0x03060000)
+    if (info.pathlike)
+    {
+        obj = PyOS_FSPath(obj);
+        if (PyErr_Occurred())
+        {
+            failmsg("Expected '%s' to be a str or path-like object", info.name);
+            return false;
+        }
+    }
+#endif
     if (getUnicodeString(obj, str))
     {
         value = str;

modules/python/src2/gen2.py

@@ -500,6 +500,10 @@ class ArgInfo(object):
     def outputarg(self):
         return '/O' in self._modifiers or '/IO' in self._modifiers
 
+    @property
+    def pathlike(self):
+        return '/PATH' in self._modifiers
+
     @property
     def returnarg(self):
         return self.outputarg
@@ -523,6 +527,7 @@ class ArgInfo(object):
     def crepr(self):
         arg  = 0x01 if self.outputarg else 0x0
         arg += 0x02 if self.arithm_op_src_arg else 0x0
+        arg += 0x04 if self.pathlike else 0x0
         return "ArgInfo(\"%s\", %d)" % (self.name, arg)
 
 

modules/python/src2/hdr_parser.py

@@ -90,6 +90,10 @@ class CppHeaderParser(object):
             modlist.append("/IO")
             arg_str = arg_str.replace("CV_IN_OUT", "")
 
+        if "CV_WRAP_FILE_PATH" in arg_str:
+            modlist.append("/PATH")
+            arg_str = arg_str.replace("CV_WRAP_FILE_PATH", "")
+
         isarray = False
         npos = arg_str.find("CV_CARRAY")
         if npos >= 0:
@@ -627,6 +631,8 @@ class CppHeaderParser(object):
                                                              ("noArray", arg_type)]).strip()
                     if '/IO' in modlist and '/O' in modlist:
                         modlist.remove('/O')
+                    if (arg_name.lower() == 'filename' or arg_name.lower() == 'filepath') and '/PATH' not in modlist:
+                        modlist.append('/PATH')
                     args.append([arg_type, arg_name, defval, modlist])
                 npos = arg_start-1
 

modules/python/test/test_pathlike.py

@@ -0,0 +1,38 @@
+from tests_common import NewOpenCVTests, unittest
+import cv2 as cv
+import os
+
+
+def import_path():
+    import sys
+    if sys.version_info[0] < 3 or sys.version_info[1] < 6:
+        raise unittest.SkipTest('Python 3.6+ required')
+
+    from pathlib import Path
+    return Path
+
+
+class CanPassPathLike(NewOpenCVTests):
+    def test_pathlib_path(self):
+        Path = import_path()
+
+        img_path = self.find_file('cv/imgproc/stuff.jpg', [os.environ.get('OPENCV_TEST_DATA_PATH')])
+
+        image_from_str = cv.imread(img_path)
+        self.assertIsNotNone(image_from_str)
+
+        image_from_path = cv.imread(Path(img_path))
+        self.assertIsNotNone(image_from_path)
+
+
+    def test_type_mismatch(self):
+        import_path() # checks python version
+
+        with self.assertRaises(TypeError) as context:
+            cv.imread(123)
+
+        self.assertTrue('str or path-like' in str(context.exception))
+
+
+if __name__ == '__main__':
+    NewOpenCVTests.bootstrap()