Allow delayed shapefile loading by passing no args, and add to tests

See #195

Author: karimbahgat

shapefile.py

@@ -802,11 +802,12 @@ def __init__(self, *args, **kwargs):
         self.__fieldposition_lookup = {}
         self.encoding = kwargs.pop('encoding', 'utf-8')
         self.encodingErrors = kwargs.pop('encodingErrors', 'strict')
-        # See if a shapefile name was passed as an argument
+        # See if a shapefile name was passed as the first argument
         if len(args) > 0:
             if is_string(args[0]):
                 self.load(args[0])
                 return
+        # Otherwise, load from separate shp/shx/dbf args (must be file-like)
         if "shp" in kwargs.keys():
             if hasattr(kwargs["shp"], "read"):
                 self.shp = kwargs["shp"]
@@ -815,6 +816,9 @@ def __init__(self, *args, **kwargs):
                     self.shp.seek(0)
                 except (NameError, io.UnsupportedOperation):
                     self.shp = io.BytesIO(self.shp.read())
+            else:
+                raise ShapefileException('The shp arg must be file-like.')
+            
             if "shx" in kwargs.keys():
                 if hasattr(kwargs["shx"], "read"):
                     self.shx = kwargs["shx"]
@@ -823,6 +827,9 @@ def __init__(self, *args, **kwargs):
                         self.shx.seek(0)
                     except (NameError, io.UnsupportedOperation):
                         self.shx = io.BytesIO(self.shx.read())
+                else:
+                    raise ShapefileException('The shx arg must be file-like.')
+                
         if "dbf" in kwargs.keys():
             if hasattr(kwargs["dbf"], "read"):
                 self.dbf = kwargs["dbf"]
@@ -831,10 +838,12 @@ def __init__(self, *args, **kwargs):
                     self.dbf.seek(0)
                 except (NameError, io.UnsupportedOperation):
                     self.dbf = io.BytesIO(self.dbf.read())
+            else:
+                raise ShapefileException('The dbf arg must be file-like.')
+            
+        # Load the files
         if self.shp or self.dbf:
             self.load()
-        else:
-            raise ShapefileException("Shapefile Reader requires a shapefile or file-like object.")
 
     def __str__(self):
         """

test_shapefile.py

@@ -291,42 +291,6 @@ def test_reader_shapefile_extension_ignored():
     assert not os.path.exists(filename)
 
 
-def test_reader_dbf_only():
-    """
-    Assert that specifying just the
-    dbf argument to the shapefile reader
-    reads just the dbf file.
-    """
-    with shapefile.Reader(dbf="shapefiles/blockgroups.dbf") as sf:
-        assert len(sf) == 663
-        record = sf.record(3)
-        assert record[1:3] == ['060750601001', 4715]
-
-
-def test_reader_shp_shx_only():
-    """
-    Assert that specifying just the
-    shp and shx argument to the shapefile reader
-    reads just the shp and shx file.
-    """
-    with shapefile.Reader(shp="shapefiles/blockgroups.shp", shx="shapefiles/blockgroups.shx") as sf:
-        assert len(sf) == 663
-        shape = sf.shape(3)
-        assert len(shape.points) is 173
-
-
-def test_reader_shx_optional():
-    """
-    Assert that specifying just the
-    shp argument to the shapefile reader
-    reads just the shp file (shx optional).
-    """
-    with shapefile.Reader(shp="shapefiles/blockgroups.shp") as sf:
-        assert len(sf) == 663
-        shape = sf.shape(3)
-        assert len(shape.points) is 173
-
-
 def test_reader_filelike_dbf_only():
     """
     Assert that specifying just the
@@ -363,6 +327,20 @@ def test_reader_filelike_shx_optional():
         assert len(shape.points) is 173
 
 
+def test_reader_shapefile_delayed_load():
+    """
+    Assert that the filename's extension is
+    ignored when reading a shapefile.
+    """
+    with shapefile.Reader() as sf:
+        # assert that data request raises exception, since no file has been provided yet
+        with pytest.raises(shapefile.ShapefileException):
+            sf.shape(0) 
+        # assert that works after loading file manually
+        sf.load("shapefiles/blockgroups")
+        assert len(sf) == 663
+
+
 def test_records_match_shapes():
     """
     Assert that the number of records matches