[AVRO-1945] Python float deviation

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Not A Bug
• Affects Version/s: 1.8.1
• Component/s: python

Environment

Python 2.7.11 with avro 1.8.1
Python 3.5.2 with avro-python3 1.8.1

• Assignee: Unassigned
• Reporter: Stephan Müller
• Created: 28/Oct/16 21:30
• Updated: 30/Oct/16 19:44
• Resolved: 28/Oct/16 22:37

Description

Unfortunately, the python avro package seems to have problems with float numbers.
After encoding data containing float values into an avro file and decoding it back, values with decimals differ a tiny bit from the original value.
In the following code sequence, the number 1.9 is saved as float. After decoding it back, the shown value is 1.899999976158142.

import avro.schema
from avro.datafile import DataFileReader, DataFileWriter
from avro.io import DatumReader, DatumWriter

schema_text = """{"namespace": "example.avro",
 "type": "record",
 "name": "Number",
 "fields": [
	 {"name": "name", "type": "string"},
	 {"name": "number",  "type": "float"}
 ]
}"""

schema = avro.schema.parse(schema_text)

writer = DataFileWriter(open("numbers.avro", "wb"), DatumWriter(), schema)
writer.append({"name": "Float number with one decimal", "number": 1.9})
writer.close()

reader = DataFileReader(open("numbers.avro", "rb"), DatumReader())
for user in reader:
	print(user)
reader.close()

Script output:

{u'name': u'Float number with one decimal', u'number': 1.899999976158142}

Using avro-tools-1.8.1.jar to decode the same created avro file (numbers.avro), the displayed floating numbers correspond to the original values:

$ java -jar avro-tools-1.8.1.jar tojson numbers.avro
{"name":"Float number with one decimal","number":{"float":1.9}}