Allow zarr.open

This demonstrates the purpose of this PR!

Now allows, for exmple `zarr.open('http://localhost:8000')`,
although there is no way to pass on further args with this method
yet.

Author: Martin Durant

zarr/creation.py

@@ -10,7 +10,7 @@
 from zarr.n5 import N5Store
 from zarr.storage import (DirectoryStore, ZipStore, contains_array,
                           contains_group, default_compressor, init_array,
-                          normalize_storage_path)
+                          normalize_storage_path, FSStore)
 
 
 def create(shape, chunks=True, dtype=None, compressor='default',
@@ -131,8 +131,10 @@ def normalize_store_arg(store, clobber=False, default=dict):
     if store is None:
         return default()
     elif isinstance(store, str):
+        mode = 'w' if clobber else 'r'
+        if "://" in store:
+            return FSStore(store)
         if store.endswith('.zip'):
-            mode = 'w' if clobber else 'r'
             return ZipStore(store, mode=mode)
         elif store.endswith('.n5'):
             return N5Store(store)

zarr/storage.py

@@ -949,13 +949,14 @@ def atexit_rmglob(path,
 class FSStore(MutableMapping):
 
     def __init__(self, url, normalize_keys=True, key_separator='.',
-                 **storage_options):
+                 mode='r', **storage_options):
         import fsspec
         self.path = url
         self.normalize_keys = normalize_keys
         self.key_separator = key_separator
         self.map = fsspec.get_mapper(url, **storage_options)
         self.fs = self.map.fs  # for direct operations
+        self.mode = mode
 
     def _normalize_key(self, key):
         key = normalize_storage_path(key)
@@ -969,6 +970,8 @@ def __getitem__(self, key):
         return self.map[key]
 
     def __setitem__(self, key, value):
+        if self.mode == 'r':
+            raise PermissionError
         key = self._normalize_key(key)
         path = self.dir_path(key)
         value = ensure_contiguous_ndarray(value)
@@ -980,6 +983,8 @@ def __setitem__(self, key, value):
             raise KeyError(key)
 
     def __delitem__(self, key):
+        if self.mode == 'r':
+            raise PermissionError
         key = self._normalize_key(key)
         path = self.dir_path(key)
         if self.fs.isdir(path):