Moved piexif into captures submodule

openflexure_microscope/captures/piexif/helper.py

@@ -0,0 +1,76 @@
+class UserComment:
+    #
+    # Names of encodings that we publicly support.
+    #
+    ASCII = "ascii"
+    JIS = "jis"
+    UNICODE = "unicode"
+    ENCODINGS = (ASCII, JIS, UNICODE)
+
+    #
+    # The actual encodings accepted by the standard library differ slightly from
+    # the above.
+    #
+    _JIS = "shift_jis"
+    _UNICODE = "utf_16_be"
+
+    _PREFIX_SIZE = 8
+    #
+    # From Table 9: Character Codes and their Designation
+    #
+    _ASCII_PREFIX = b"\x41\x53\x43\x49\x49\x00\x00\x00"
+    _JIS_PREFIX = b"\x4a\x49\x53\x00\x00\x00\x00\x00"
+    _UNICODE_PREFIX = b"\x55\x4e\x49\x43\x4f\x44\x45\x00"
+    _UNDEFINED_PREFIX = b"\x00\x00\x00\x00\x00\x00\x00\x00"
+
+    @classmethod
+    def load(cls, data):
+        """
+        Convert "UserComment" value in exif format to str.
+
+        :param bytes data: "UserComment" value from exif
+        :return: u"foobar"
+        :rtype: str(Unicode)
+        :raises: ValueError if the data does not conform to the EXIF specification,
+        or the encoding is unsupported.
+        """
+        if len(data) < cls._PREFIX_SIZE:
+            raise ValueError("not enough data to decode UserComment")
+        prefix = data[: cls._PREFIX_SIZE]
+        body = data[cls._PREFIX_SIZE :]
+        if prefix == cls._UNDEFINED_PREFIX:
+            raise ValueError("prefix is UNDEFINED, unable to decode UserComment")
+        try:
+            encoding = {
+                cls._ASCII_PREFIX: cls.ASCII,
+                cls._JIS_PREFIX: cls._JIS,
+                cls._UNICODE_PREFIX: cls._UNICODE,
+            }[prefix]
+        except KeyError as e:
+            raise ValueError("unable to determine appropriate encoding") from e
+        return body.decode(encoding, errors="replace")
+
+    @classmethod
+    def dump(cls, data, encoding="ascii"):
+        """
+        Convert str to appropriate format for "UserComment".
+
+        :param data: Like u"foobar"
+        :param str encoding: "ascii", "jis", or "unicode"
+        :return: b"ASCII\x00\x00\x00foobar"
+        :rtype: bytes
+        :raises: ValueError if the encoding is unsupported.
+        """
+        if encoding not in cls.ENCODINGS:
+            raise ValueError(
+                "encoding %r must be one of %r" % (encoding, cls.ENCODINGS)
+            )
+        prefix = {
+            cls.ASCII: cls._ASCII_PREFIX,
+            cls.JIS: cls._JIS_PREFIX,
+            cls.UNICODE: cls._UNICODE_PREFIX,
+        }[encoding]
+        internal_encoding = {cls.UNICODE: cls._UNICODE, cls.JIS: cls._JIS}.get(
+            encoding, encoding
+        )
+        return prefix + data.encode(internal_encoding, errors="replace")