Add more documentation (open-telemetry#2641)

Fixes open-telemetry#2129

opentelemetry-api/src/opentelemetry/_metrics/instrument.py

@@ -98,10 +98,12 @@ def __init__(
 
 
 class Synchronous(Instrument):
-    pass
+    """Base class for all synchronous instruments"""
 
 
 class Asynchronous(Instrument):
+    """Base class for all asynchronous instruments"""
+
     @abstractmethod
     def __init__(
         self,

opentelemetry-sdk/src/opentelemetry/sdk/_metrics/__init__.py

@@ -55,6 +55,8 @@
 
 
 class Meter(APIMeter):
+    """See `opentelemetry._metrics.Meter`."""
+
     def __init__(
         self,
         instrumentation_scope: InstrumentationScope,

opentelemetry-sdk/src/opentelemetry/sdk/_metrics/export/__init__.py

@@ -35,6 +35,10 @@
 
 
 class MetricExportResult(Enum):
+    """Result of exporting a metric
+
+    Can be any of the following values:"""
+
     SUCCESS = 0
     FAILURE = 1
 

opentelemetry-sdk/src/opentelemetry/sdk/_metrics/measurement.py

@@ -23,6 +23,10 @@
 
 @dataclass(frozen=True)
 class Measurement:
+    """
+    Represents a data point reported via the metrics API to the SDK.
+    """
+
     value: Union[int, float]
     instrument: "_Instrument"
     attributes: Attributes = None

opentelemetry-sdk/src/opentelemetry/sdk/_metrics/point.py

@@ -23,13 +23,22 @@
 
 
 class AggregationTemporality(IntEnum):
+    """
+    The temporality to use when aggregating data.
+
+    Can be one of the following values:
+    """
+
     UNSPECIFIED = 0
     DELTA = 1
     CUMULATIVE = 2
 
 
 @dataclass(frozen=True)
 class Sum:
+    """Represents the type of a scalar metric that is calculated as a sum of
+    all reported measurements over a time interval."""
+
     aggregation_temporality: AggregationTemporality
     is_monotonic: bool
     start_time_unix_nano: int
@@ -39,12 +48,19 @@ class Sum:
 
 @dataclass(frozen=True)
 class Gauge:
+    """Represents the type of a scalar metric that always exports the current
+    value for every data point. It should be used for an unknown
+    aggregation."""
+
     time_unix_nano: int
     value: Union[int, float]
 
 
 @dataclass(frozen=True)
 class Histogram:
+    """Represents the type of a metric that is calculated by aggregating as a
+    histogram of all reported measurements over a time interval."""
+
     aggregation_temporality: AggregationTemporality
     bucket_counts: Sequence[int]
     explicit_bounds: Sequence[float]