libtiff_ctype: On Windows, use TIFFOpenW() when open() gets a str

Depending the Windows encoding, it can be impossible to encode a unicode
path into the "filesystem encoding". So instead of employing all sorts
of hacks, just use the designated function which directly takes unicode
input. This has the advantage of being much more reliable.

Also drop Python 2 support, as it's no needed anymore.

libtiff/libtiff_ctypes.py

@@ -17,6 +17,7 @@
 import struct
 import collections
 import locale
+import warnings
 
 __all__ = ['libtiff', 'TIFF']
 
@@ -524,24 +525,32 @@ def get_tag_define(tagname):
     @classmethod
     def open(cls, filename, mode='r'):
         """ Open tiff file as TIFF.
+
+        Parameters
+        ----------
+        filename: str or bytes.
+          The path to the file.
+        mode: str
+          Specifies if the file is to be opened for reading ('r'), writing ('w'),
+          or appending ('a'). Optional flags can be passed. See the documentation
+          of TIFFOpen() for the complete list.
         """
-        try:
+        if isinstance(filename, str) and hasattr(libtiff, "TIFFOpenW"):
+            # On Windows, the only reliable way to open a file with unicode characters
+            # is to use the *W function.
+            # It needs a str for the argument of type "c_wchar_p"
+            tiff = libtiff.TIFFOpenW(filename, mode.encode('ascii'))
+        else:
+            # It needs bytes for the argument of type "c_char_p"
             try:
-                # Python3: it needs bytes for the arguments of type "c_char_p"
-                if isinstance(filename, str) and 'win' in sys.platform:
-                    filename = filename.encode(locale.getpreferredencoding(False))
-                else:
-                    filename = os.fsencode(filename)  # no-op if already bytes
-            except AttributeError:
-                # Python2: it needs str for the arguments of type "c_char_p"
-                if isinstance(filename, unicode):  # noqa: F821
-                    filename = filename.encode(sys.getfilesystemencoding())
-        except Exception as ex:
-            # It's probably going to not work, but let it try
-            print('Warning: filename argument is of wrong type or encoding: %s'
-                  % ex)
-
-        tiff = libtiff.TIFFOpen(filename, mode.encode('ascii'))
+                filename = os.fsencode(os.fspath(filename))  # no-op if already bytes
+            except UnicodeError as ex:
+                # It's probably not going to work, but let's try
+                warnings.warn(f"Warning: filename argument is of wrong type or "
+                              f"encoding for the filesystem: {ex}")
+
+            tiff = libtiff.TIFFOpen(filename, mode.encode('ascii'))
+
         if tiff.value is None:
             raise TypeError('Failed to open file ' + repr(filename))
         return tiff
@@ -1648,39 +1657,18 @@ class TIFF3D(TIFF):
     def open(cls, filename, mode='r'):
         """ just like TIFF.open, except returns a TIFF3D instance.
         """
-        try:
-            try:
-                # Python3: it needs bytes for the arguments of type "c_char_p"
-                if isinstance(filename, str) and 'win' in sys.platform:
-                    filename = filename.encode(locale.getpreferredencoding(False))
-                else:
-                    filename = os.fsencode(filename)  # no-op if already bytes
-            except AttributeError:
-                # Python2: it needs str for the arguments of type "c_char_p"
-                if isinstance(filename, unicode):  # noqa: F821
-                    filename = filename.encode(sys.getfilesystemencoding())
-        except Exception as ex:
-            # It's probably going to not work, but let it try
-            print('Warning: filename argument is of wrong type or encoding: %s'
-                  % ex)
-        if isinstance(mode, str):
-            mode = mode.encode()
-
         # monkey-patch the restype:
-        old_restype = libtiff.TIFFOpen.restype
         libtiff.TIFFOpen.restype = TIFF3D
+        if hasattr(libtiff, "TIFFOpenW"):
+            libtiff.TIFFOpenW.restype = TIFF3D
+
         try:
-            # actually call the library function:
-            tiff = libtiff.TIFFOpen(filename, mode)
-        except Exception:
-            raise
+            return super().open(filename, mode)
         finally:
             # restore the old restype:
-            libtiff.TIFFOpen.restype = old_restype
-
-        if tiff.value is None:
-            raise TypeError('Failed to open file ' + repr(filename))
-        return tiff
+            libtiff.TIFFOpen.restype = TIFF
+            if hasattr(libtiff, "TIFFOpenW"):
+                libtiff.TIFFOpenW.restype = TIFF
 
     @debug
     def read_image(self, verbose=False, as3d=True):
@@ -1789,6 +1777,10 @@ def __str__(self):
 libtiff.TIFFOpen.restype = TIFF
 libtiff.TIFFOpen.argtypes = [ctypes.c_char_p, ctypes.c_char_p]
 
+if hasattr(libtiff, "TIFFOpenW"):  # Windows-only
+    libtiff.TIFFOpenW.restype = TIFF
+    libtiff.TIFFOpenW.argtypes = [ctypes.c_wchar_p, ctypes.c_char_p]
+
 libtiff.TIFFFileName.restype = ctypes.c_char_p
 libtiff.TIFFFileName.argtypes = [TIFF]