docs: add an example: How to use RxPY to prepare batches by maximum bytes count.

Author: bednar

examples/README.md

@@ -9,6 +9,7 @@
 - [import_data_set_sync_batching.py](import_data_set_sync_batching.py) - How to use [RxPY](https://rxpy.readthedocs.io/en/latest/) to prepare batches for synchronous write into InfluxDB
 - [write_api_callbacks.py](write_api_callbacks.py) - How to handle batch events
 - [write_structured_data.py](write_structured_data.py) - How to write structured data - [NamedTuple](https://docs.python.org/3/library/collections.html#collections.namedtuple), [Data Classes](https://docs.python.org/3/library/dataclasses.html) - (_requires Python v3.8+_)
+- [write_batching_by_bytes_count.py](write_batching_by_bytes_count.py) - How to use RxPY to prepare batches by maximum bytes count.
 
 ## Queries
 - [query.py](query.py) - How to query data into `FluxTable`s, `Stream` and `CSV`

examples/write_batching_by_bytes_count.py

@@ -0,0 +1,116 @@
+"""
+How to use RxPY to prepare batches by maximum bytes count.
+"""
+
+from csv import DictReader
+from functools import reduce
+from typing import Collection
+
+import rx
+from rx import operators as ops, Observable
+
+from influxdb_client import InfluxDBClient, Point
+from influxdb_client.client.write.retry import WritesRetry
+from influxdb_client.client.write_api import SYNCHRONOUS
+
+
+def csv_to_generator(csv_file_path):
+    """
+    Parse your CSV file into generator
+    """
+    for row in DictReader(open(csv_file_path, 'r')):
+        point = Point('financial-analysis') \
+            .tag('type', 'vix-daily') \
+            .field('open', float(row['VIX Open'])) \
+            .field('high', float(row['VIX High'])) \
+            .field('low', float(row['VIX Low'])) \
+            .field('close', float(row['VIX Close'])) \
+            .time(row['Date'])
+        yield point
+
+
+def _buffer_bytes_size(buffer: Collection['bytes']):
+    """
+    Calculate size of buffer
+    """
+    return reduce(lambda total, actual: total + actual, map(lambda x: len(x), buffer)) + (
+        len(buffer))
+
+
+def buffer_by_bytes_count(bytes_count: int = 5120):
+    """
+    Buffer emitted items until the byte count is reached.
+    """
+
+    def _buffer_by_bytes_count(source: Observable) -> Observable:
+        def subscribe(observer, scheduler=None):
+            observer.buffer = []
+
+            def on_next(current):
+                observer.buffer.append(current)
+                # Emit new batch if the buffer size is greater then boundary
+                if (_buffer_bytes_size(observer.buffer) + len(current)) >= bytes_count:
+                    # emit batch
+                    observer.on_next(observer.buffer)
+                    observer.buffer = []
+
+            def on_error(exception):
+                observer.buffer = []
+                observer.on_error(exception)
+
+            def on_completed():
+                if len(observer.buffer) >= 0:
+                    # flush rest of buffer
+                    observer.on_next(observer.buffer)
+                    observer.buffer = []
+                observer.on_completed()
+
+            return source.subscribe(
+                on_next,
+                on_error,
+                on_completed,
+                scheduler)
+
+        return Observable(subscribe)
+
+    return _buffer_by_bytes_count
+
+
+"""
+Define Retry strategy - 3 attempts => 2, 4, 8
+"""
+retries = WritesRetry(total=3, retry_interval=1, exponential_base=2)
+with InfluxDBClient(url='http://localhost:8086', token='my-token', org='my-org', retries=retries) as client:
+    """
+    Use synchronous version of WriteApi to strongly depends on result of write
+    """
+    write_api = client.write_api(write_options=SYNCHRONOUS)
+
+    """
+    Prepare batches from generator:
+     1. Map Point into LineProtocol
+     2. Map LineProtocol into bytes
+     3. Create batches by bytes count - 5120 - 5KiB
+    """
+    batches = rx \
+        .from_iterable(csv_to_generator('vix-daily.csv')) \
+        .pipe(ops.map(lambda point: point.to_line_protocol())) \
+        .pipe(ops.map(lambda line_protocol: line_protocol.encode("utf-8"))) \
+        .pipe(buffer_by_bytes_count(bytes_count=5120))
+
+
+    def write_batch(batch):
+        """
+        Synchronous write
+        """
+        print(f'Writing batch...')
+        write_api.write(bucket='my-bucket', record=batch)
+        print(f' > {_buffer_bytes_size(batch)} bytes')
+
+
+    """
+    Write batches
+    """
+    batches.subscribe(on_next=lambda batch: write_batch(batch),
+                      on_error=lambda ex: print(f'Unexpected error: {ex}'),
+                      on_completed=lambda: print('Import finished!'))