Makes geopandas an optional dependency (#10)

* Makes geopandas an optional dependency

* import geopandas when required

Co-authored-by: Eddy <Edward.Comyn-Platt@ecmwf.int>

emohawk/readers/shapefile.py

@@ -6,9 +6,6 @@
 # granted to it by virtue of its status as an intergovernmental organisation
 # nor does it submit to any jurisdiction.
 
-
-import geopandas as gpd
-
 from . import Reader
 
 
@@ -17,6 +14,9 @@ class ShapefileReader(Reader):
     Class for reading and polymorphing ESRI Shapefiles.
     """
 
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+
     def to_pandas(self, **kwargs):
         """
         Return a pandas `dataframe` representation of the data.
@@ -25,6 +25,8 @@ def to_pandas(self, **kwargs):
         -------
         pandas.core.frame.DataFrame
         """
+        import geopandas as gpd
+
         return gpd.read_file(self.source, **kwargs)
 
     def to_json(self, file_name):