Add some typings informations and typecheck

Mostly make it a bit clearer what is allowed/expected where.
In particular many of the decode fucntions allow already decoded
objects.

Author: Carreau

.travis.yml

@@ -33,6 +33,7 @@ matrix:
     - python: 3.8
       dist: xenial
       sudo: true
+      env: MYPY_CHECK='true'
 
 before_install:
   - docker pull arafato/azurite
@@ -42,11 +43,12 @@ before_script:
     - mongo mydb_test --eval 'db.createUser({user:"travis",pwd:"test",roles:["readWrite"]});'
 
 install:
-  - pip install -U pip setuptools wheel tox-travis coveralls
+  - pip install -U pip setuptools wheel tox-travis coveralls mypy
 
 script:
   - tox
   - if [[ $BUILD_DOCS == 'true' ]]; then tox -e docs; fi
+  - if [[ $MYPY_CHECK == 'true' ]]; then mypy zarr; fi
 
 after_success:
   - coveralls --service=travis-pro

mypy.ini

@@ -0,0 +1,4 @@
+[mypy]
+python_version = 3.6
+ignore_missing_imports = True
+follow_imports = silent

zarr/codecs.py

@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
 # flake8: noqa
 from numcodecs import *
+from numcodecs import get_codec, Blosc, Zlib, Delta, AsType, BZ2
 from numcodecs.registry import codec_registry

zarr/meta.py

@@ -7,10 +7,12 @@
 from zarr.errors import MetadataError
 from zarr.util import json_dumps, json_loads
 
+from typing import Union, Any
+
 ZARR_FORMAT = 2
 
 
-def parse_metadata(s):
+def parse_metadata(s: Union[Mapping, str]) -> Mapping[str, Any]:
 
     # Here we allow that a store may return an already-parsed metadata object,
     # or a string of JSON that we will parse here. We allow for an already-parsed
@@ -28,7 +30,7 @@ def parse_metadata(s):
     return meta
 
 
-def decode_array_metadata(s):
+def decode_array_metadata(s: Union[Mapping, str]) -> Mapping[str, Any]:
     meta = parse_metadata(s)
 
     # check metadata format
@@ -56,7 +58,7 @@ def decode_array_metadata(s):
         return meta
 
 
-def encode_array_metadata(meta):
+def encode_array_metadata(meta: Mapping[str, Any]) -> str:
     dtype = meta['dtype']
     sdshape = ()
     if dtype.subdtype is not None:
@@ -74,7 +76,7 @@ def encode_array_metadata(meta):
     return json_dumps(meta)
 
 
-def encode_dtype(d):
+def encode_dtype(d) -> str:
     if d.fields is None:
         return d.str
     else: