workaournd writef() on pypy3

pypy3's BufferedReader don't have __sizeof__()
so alternatively calculate it with seek() and tell()

Signed-off-by: Hiroshi Miura <miurahr@linux.com>

py7zr/py7zr.py

@@ -917,13 +917,21 @@ def writef(self, bio: BinaryIO, arcname: str):
         elif isinstance(bio, io.TextIOBase):
             # First check whether is it Text?
             raise ValueError("Unsupported file object type: please open file with Binary mode.")
-        elif isinstance(bio, io.BufferedIOBase):
-            size = bio.__sizeof__()
         elif hasattr(bio, "read") and hasattr(bio, "__sizeof__"):
-            # Allow objet type which has read() and length methods for duck typing
+            # CPython's io.BufferedIOBase or io.BufferedReader has __sizeof__, but
+            # pypy3 don't have. So first check __sizeof__ and then goes to alternative.
+            # Also allowing objet type which has read() and length methods for duck typing
             size = bio.__sizeof__()
+        elif isinstance(bio, io.BufferedIOBase):
+            # come here when subtype of io.BufferedIOBase that don't have __sizeof__ (eg. pypy)
+            # alternative for `size = bio.__sizeof__()`
+            current = bio.tell()
+            bio.seek(0, os.SEEK_END)
+            last = bio.tell()
+            bio.seek(current, os.SEEK_SET)
+            size = last - current
         else:
-            raise ValueError("Wrong argument passed for bio.")
+            raise ValueError("Wrong argument passed for argument bio.")
         file_info = self._make_file_info_from_name(bio, size, arcname)
         self.header.files_info.files.append(file_info)
         self.header.files_info.emptyfiles.append(file_info['emptystream'])