Add nancodes enum util

Author: dshemetov

_delphi_utils_python/delphi_utils/__init__.py

@@ -12,5 +12,6 @@
 from .geomap import GeoMapper
 from .smooth import Smoother
 from .signal import add_prefix
+from .nancodes import Nans
 
 __version__ = "0.1.0"

_delphi_utils_python/delphi_utils/nancodes.py

@@ -0,0 +1,19 @@
+"""Unified not-a-number codes for the indicators.
+
+Currently requires a manual sync between the covidcast-indicators
+and the delphi-epidata repo.
+* in covidcast-indicators: _delphi_utils_python/delphi_utils
+* in delphi-epidata: src/acquisition/covidcast
+"""
+
+from enum import IntEnum
+
+class Nans(IntEnum):
+    """An enum of not-a-number codes for the indicators."""
+
+    NOT_MISSING = 0
+    NOT_APPLICABLE = 1
+    REGION_EXCEPTION = 2
+    PRIVACY = 3
+    DELETED = 4
+    UNKNOWN = 5