fastavro man page

class reader(fo, reader_schema=None)

Iterator over records in an avro file.

Parameters

• fo (file-like) – Input stream
• reader_schema (dict, optional) – Reader schema

Example:

from fastavro import reader
with open('some-file.avro', 'rb') as fo:
    avro_reader = reader(fo)
    for record in avro_reader:
        process_record(record)

metadata

Key-value pairs in the header metadata

codec

The codec used when writing

writer_schema

The schema used when writing

reader_schema

The schema used when reading (if provided)

class block_reader(fo, reader_schema=None)

Iterator over Block in an avro file.

Parameters

• fo (file-like) – Input stream
• reader_schema (dict, optional) – Reader schema

Example:

from fastavro import block_reader
with open('some-file.avro', 'rb') as fo:
    avro_reader = block_reader(fo)
    for block in avro_reader:
        process_block(block)

metadata

Key-value pairs in the header metadata

codec

The codec used when writing

writer_schema

The schema used when writing

reader_schema

The schema used when reading (if provided)

class Block(bytes_, num_records, codec, reader_schema, writer_schema, offset, size)

An avro block. Will yield records when iterated over

num_records

Number of records in the block

writer_schema

The schema used when writing

reader_schema

The schema used when reading (if provided)

offset

Offset of the block from the begining of the avro file

size

Size of the block in bytes

schemaless_reader(fo, writer_schema, reader_schema=None)

Reads a single record writen using the schemaless_writer()

Parameters

• fo (file-like) – Input stream
• writer_schema (dict) – Schema used when calling schemaless_writer
• reader_schema (dict, optional) – If the schema has changed since being written then the new schema can be given to allow for schema migration

Example:

parsed_schema = fastavro.parse_schema(schema)
with open('file.avro', 'rb') as fp:
    record = fastavro.schemaless_reader(fp, parsed_schema)

Note: The schemaless_reader can only read a single record.

is_avro(path_or_buffer)

Return True if path (or buffer) points to an Avro file.

Parameters

path_or_buffer (path to file or file-like object) – Path to file

writer(fo, schema, records, codec='null', sync_interval=16000, metadata=None, validator=None, sync_marker=None)

Write records to fo (stream) according to schema

Parameters

• fo (file-like) – Output stream
• records (iterable) – Records to write. This is commonly a list of the dictionary representation of the records, but it can be any iterable
• codec (string, optional) – Compression codec, can be ‘null’, ‘deflate’ or ‘snappy’ (if installed)
• sync_interval (int, optional) – Size of sync interval
• metadata (dict, optional) – Header metadata
• validator (None, True or a function) – Validator function. If None (the default) - no validation. If True then then fastavro.validation.validate will be used. If it’s a function, it should have the same signature as fastavro.writer.validate and raise an exeption on error.
• sync_marker (bytes, optional) – A byte string used as the avro sync marker. If not provided, a random byte string will be used.

Example:

from fastavro import writer, parse_schema

schema = {
    'doc': 'A weather reading.',
    'name': 'Weather',
    'namespace': 'test',
    'type': 'record',
    'fields': [
        {'name': 'station', 'type': 'string'},
        {'name': 'time', 'type': 'long'},
        {'name': 'temp', 'type': 'int'},
    ],
}
parsed_schema = parse_schema(schema)

records = [
    {u'station': u'011990-99999', u'temp': 0, u'time': 1433269388},
    {u'station': u'011990-99999', u'temp': 22, u'time': 1433270389},
    {u'station': u'011990-99999', u'temp': -11, u'time': 1433273379},
    {u'station': u'012650-99999', u'temp': 111, u'time': 1433275478},
]

with open('weather.avro', 'wb') as out:
    writer(out, parsed_schema, records)

Given an existing avro file, it’s possible to append to it by re-opening the file in a+b mode. If the file is only opened in ab mode, we aren’t able to read some of the existing header information and an error will be raised. For example:

# Write initial records
with open('weather.avro', 'wb') as out:
    writer(out, parsed_schema, records)

# Write some more records
with open('weather.avro', 'a+b') as out:
    writer(out, parsed_schema, more_records)

schemaless_writer(fo, schema, record)

Write a single record without the schema or header information

Parameters

• fo (file-like) – Output file
• schema (dict) – Schema
• record (dict) – Record to write

Example:

parsed_schema = fastavro.parse_schema(schema)
with open('file.avro', 'rb') as fp:
    fastavro.schemaless_writer(fp, parsed_schema, record)

Note: The schemaless_writer can only write a single record.

parse_schema(schema, _write_hint=True, _force=False)

Returns a parsed avro schema

It is not necessary to call parse_schema but doing so and saving the parsed schema for use later will make future operations faster as the schema will not need to be reparsed.

Parameters

• schema (dict) – Input schema
• _write_hint (bool) – Internal API argument specifying whether or not the __fastavro_parsed marker should be added to the schema
• _force (bool) – Internal API argument. If True, the schema will always be parsed even if it has been parsed and has the __fastavro_parsed marker

Example:

from fastavro import parse_schema
from fastavro import writer

parsed_schema = parse_schema(original_schema)
with open('weather.avro', 'wb') as out:
    writer(out, parsed_schema, records)

validate(datum, schema, field=None, raise_errors=True)

Determine if a python datum is an instance of a schema.

Parameters

• datum (Any) – Data being validated
• schema (dict) – Schema
• field (str, optional) – Record field being validated
• raise_errors (bool, optional) – If true, errors are raised for invalid data. If false, a simple True (valid) or False (invalid) result is returned

Example:

from fastavro.validation import validate
schema = {...}
record = {...}
validate(record, schema)

validate_many(records, schema, raise_errors=True)

Validate a list of data!

Parameters

• records (iterable) – List of records to validate
• schema (dict) – Schema
• raise_errors (bool, optional) – If true, errors are raised for invalid data. If false, a simple True (valid) or False (invalid) result is returned

Example:

from fastavro.validation import validate_many
schema = {...}
records = [{...}, {...}, ...]
validate_many(records, schema)

A command line script is installed with the library that can be used to dump the contents of avro file(s) to the standard output.

Usage:

usage: fastavro [-h] [--schema] [--codecs] [--version] [-p] [file [file ...]]

iter over avro file, emit records as JSON

positional arguments:
  file          file(s) to parse

optional arguments:
  -h, --help    show this help message and exit
  --schema      dump schema instead of records
  --codecs      print supported codecs
  --version     show program's version number and exit
  -p, --pretty  pretty print json

Read an avro file:

$ fastavro weather.avro

{"temp": 0, "station": "011990-99999", "time": -619524000000}
{"temp": 22, "station": "011990-99999", "time": -619506000000}
{"temp": -11, "station": "011990-99999", "time": -619484400000}
{"temp": 111, "station": "012650-99999", "time": -655531200000}
{"temp": 78, "station": "012650-99999", "time": -655509600000}

Show the schema:

$ fastavro --schema weather.avro

{
 "type": "record",
 "namespace": "test",
 "doc": "A weather reading.",
 "fields": [
  {
   "type": "string",
   "name": "station"
  },
  {
   "type": "long",
   "name": "time"
  },
  {
   "type": "int",
   "name": "temp"
  }
 ],
 "name": "Weather"
}

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