crs of dataset with no SRS is None

str(CRS()) == ''

Resolves #1616

CHANGES.txt

@@ -1,15 +1,17 @@
 Changes
 =======
 
-Next (?)
---------
+1.0.16 (2019-02-04)
+-------------------
 
 - A bug preventing GCPs from being created with new BufferedDatasetWriter
   instances (#1600) has been fixed (#1610).
 - A previously unreported bug preventing BufferedDatasetWriters from being
   opened in r+ mode has been fixed.
 - A regression in creating CRS objects from PROJ4 strings that include
   "+wktext" (#1609) has been fixed.
+- Regressions in str representations of empty CRS objects and the handling of
+  unreferenced datasets in rasterio._base have been fixed (#1616).
 
 1.0.15 (2019-01-27)
 -------------------

rasterio/_base.pyx

@@ -267,7 +267,7 @@ cdef class DatasetBase(object):
         if wkt:
             return CRS.from_wkt(wkt)
         else:
-            return CRS()
+            return None
 
     def read_crs(self):
         """Return the GDAL dataset's stored CRS"""

rasterio/crs.py

@@ -167,11 +167,18 @@ def to_dict(self):
         dict
 
         """
-        epsg_code = self.to_epsg()
-        if epsg_code:
-            return {'init': 'epsg:{}'.format(epsg_code)}
+        if self._crs is None:
+            raise CRSError("Undefined CRS has no dict representation")
+
         else:
-            return self._crs.to_dict()
+            epsg_code = self.to_epsg()
+            if epsg_code:
+                return {'init': 'epsg:{}'.format(epsg_code)}
+            else:
+                try:
+                    return self._crs.to_dict()
+                except CRSError:
+                    return {}
 
     @property
     def data(self):

tests/test_crs.py

@@ -88,6 +88,12 @@ def test_read_esri_wkt():
         }
 
 
+def test_read_no_crs():
+    """crs of a dataset with no SRS is None"""
+    with rasterio.open('tests/data/389225main_sw_1965_1024.jpg') as src:
+        assert src.crs is None
+
+
 # Ensure that CRS sticks when we write a file.
 @pytest.mark.gdalbin
 def test_write_3857(tmpdir):
@@ -415,3 +421,8 @@ def test_issue1609_wktext_b():
                'wktext': True}
     wkt = CRS(dst_proj).wkt
     assert 'EXTENSION["PROJ4","+ellps=WGS84 +h=9000000.0 +lat_0=-78.0 +lon_0=0.0 +proj=nsper +units=m +x_0=0 +y_0=0 +wktext"]]' in wkt
+
+
+def test_empty_crs_str():
+    """str(CRS()) should be empty string"""
+    assert str(CRS()) == ''