Fix Python 3.7 deprecation warnings

.travis.yml

@@ -4,6 +4,8 @@ python:
 - 2.7
 - 3.5
 - 3.6
+- 3.7
+- 3.8
 - pypy
 cache: pip
 install:
@@ -15,7 +17,7 @@ after_success:
 matrix:
   fast_finish: true
   include:
-  - python: '3.6'
+  - python: '3.8'
     script: |
       # pip install pyre-check
       # pyre --source-directory promise check

promise/dataloader.py

@@ -1,4 +1,8 @@
-from collections import Iterable, namedtuple
+from collections import namedtuple
+try:
+    from collections.abc import Iterable
+except ImportError:
+    from collections import Iterable
 from functools import partial
 
 from .promise import Promise, async_instance, get_default_scheduler
@@ -67,16 +71,12 @@ def __init__(
         if cache is not None:
             self.cache = cache
 
-        if get_cache_key is not None:
-            self.get_cache_key = get_cache_key
+        self.get_cache_key = get_cache_key or (lambda x: x)
 
         self._promise_cache = cache_map or {}
         self._queue = []  # type: List[Loader]
         self._scheduler = scheduler
 
-    def get_cache_key(self, key):  # type: ignore
-        return key
-
     def load(self, key=None):
         # type: (Hashable) -> Promise
         """
@@ -227,7 +227,7 @@ def on_promise_resolve(v):
         # type: (Any) -> None
         async_instance.invoke(fn, scheduler)
 
-    resolved_promise.then(on_promise_resolve)  # type: Promise[None]
+    resolved_promise.then(on_promise_resolve) 
 
 
 def dispatch_queue(loader):

promise/promise.py

@@ -319,7 +319,7 @@ def _settle_promise(
                 if async_guaranteed:
                     promise._is_async_guaranteed = True  # type: ignore
                 self._settle_promise_from_handler(  # type: ignore
-                    handler, value, promise
+                    handler, value, promise  # type: ignore
                 )  # type: ignore
         elif is_promise:
             if async_guaranteed:
@@ -567,7 +567,7 @@ def _then(
         did_reject=None,  # type: Optional[Callable[[Exception], S]]
     ):
         # type: (...) -> Promise[S]
-        promise = self.__class__()
+        promise = self.__class__()  # type: Promise
         target = self._target()
 
         state = target._state
@@ -791,7 +791,7 @@ def for_dict(cls, m):
         dict_type = type(m)  # type: Type[Dict]
 
         if not m:
-            return cls.resolve(dict_type())
+            return cls.resolve(dict_type())  # type: ignore
 
         def handle_success(resolved_values):
             # type: (List[S]) -> Dict[Hashable, S]

promise/promise_list.py

@@ -1,5 +1,8 @@
 from functools import partial
-from collections import Iterable
+try:
+    from collections.abc import Iterable
+except ImportError:
+    from collections import Iterable
 
 if False:
     from .promise import Promise

setup.py

@@ -45,6 +45,9 @@
         "Programming Language :: Python :: 3.3",
         "Programming Language :: Python :: 3.4",
         "Programming Language :: Python :: 3.5",
+        "Programming Language :: Python :: 3.6",
+        "Programming Language :: Python :: 3.7",
+        "Programming Language :: Python :: 3.8",
         "Programming Language :: Python :: Implementation :: PyPy",
         "License :: OSI Approved :: MIT License",
     ],