py3: add docx.compat.is_string()

Steve Canny · Steve Canny · commit 6de44263275e · 2014-01-07T02:55:16.000-08:00
diff --git a/docx/compat.py b/docx/compat.py
@@ -18,10 +18,22 @@
 
     from io import BytesIO
 
+    def is_string(obj):
+        """
+        Return True if *obj* is a string, False otherwise.
+        """
+        return isinstance(obj, str)
+
 # ===========================================================================
 # Python 2 versions
 # ===========================================================================
 
 else:
 
     from StringIO import StringIO as BytesIO  # noqa
+
+    def is_string(obj):
+        """
+        Return True if *obj* is a string, False otherwise.
+        """
+        return isinstance(obj, basestring)
diff --git a/docx/parts/image.py b/docx/parts/image.py
@@ -16,7 +16,7 @@
 except ImportError:
     import Image as PIL_Image
 
-from docx.compat import BytesIO
+from docx.compat import BytesIO, is_string
 from docx.opc.constants import CONTENT_TYPE as CT
 from docx.opc.package import Part
 from docx.shared import Emu, Inches, lazyproperty
@@ -80,7 +80,7 @@ def from_file(cls, image_descriptor):
         Return a new |Image| instance loaded from the image file identified
         by *image_descriptor*, a path or file-like object.
         """
-        if isinstance(image_descriptor, basestring):
+        if is_string(image_descriptor):
             path = image_descriptor
             with open(path, 'rb') as f:
                 blob = f.read()
