hiredis-py
Python extension that wraps protocol parsing code in hiredis.
It primarily speeds up parsing of multi bulk replies.
Install
hiredis-py is available on PyPI, and can
be installed with:
pip install hiredis
Requirements
hiredis-py requires Python 2.7 or 3.4+.
Make sure Python development headers are available when installing hiredis-py.
On Ubuntu/Debian systems, install them with apt-get install python-dev for Python 2
or apt-get install python3-dev for Python 3.
Usage
The hiredis module contains the Reader class. This class is responsible for
parsing replies from the stream of data that is read from a Redis connection.
It does not contain functionality to handle I/O.
Reply parser
The Reader class has two methods that are used when parsing replies from a
stream of data. Reader.feed takes a string argument that is appended to the
internal buffer. Reader.gets reads this buffer and returns a reply when the
buffer contains a full reply. If a single call to feed contains multiple
replies, gets should be called multiple times to extract all replies.
Example:
>>> reader = hiredis.Reader()
>>> reader.feed("$5\r\nhello\r\n")
>>> reader.gets()
'hello'
When the buffer does not contain a full reply, gets returns False. This
means extra data is needed and feed should be called again before calling
gets again:
>>> reader.feed("*2\r\n$5\r\nhello\r\n")
>>> reader.gets()
False
>>> reader.feed("$5\r\nworld\r\n")
>>> reader.gets()
['hello', 'world']
Unicode
hiredis.Reader is able to decode bulk data to any encoding Python supports.
To do so, specify the encoding you want to use for decoding replies when
initializing it:
>>> reader = hiredis.Reader(encoding="utf-8", errors="strict")
>>> reader.feed("$3\r\n\xe2\x98\x83\r\n")
>>> reader.gets()
u'☃'
Decoding of bulk data will be attempted using the specified encoding and
error handler. If the error handler is 'strict' (the default), a
UnicodeDecodeError is raised when data cannot be dedcoded. This is identical
to Python's default behavior. Other valid values to errors include
'replace', 'ignore', and 'backslashreplace'. More information on the
behavior of these error handlers can be found
here.
When the specified encoding cannot be found, a LookupError will be raised
when calling gets for the first reply with bulk data.
Error handling
When a protocol error occurs (because of multiple threads using the same
socket, or some other condition that causes a corrupt stream), the error
hiredis.ProtocolError is raised. Because the buffer is read in a lazy
fashion, it will only be raised when gets is called and the first reply in
the buffer contains an error. There is no way to recover from a faulty protocol
state, so when this happens, the I/O code feeding data to Reader should
probably reconnect.
Redis can reply with error replies (-ERR ...). For these replies, the custom
error class hiredis.ReplyError is returned, but not raised.
When other error types should be used (so existing code doesn't have to change
its except clauses), Reader can be initialized with the protocolError and
replyError keywords. These keywords should contain a class that is a
subclass of Exception. When not provided, Reader will use the default
error types.
Benchmarks
The repository contains a benchmarking script in the benchmark directory,
which uses gevent to have non-blocking I/O and redis-py
to handle connections. These benchmarks are done with a patched version of
redis-py that uses hiredis-py when it is available.
All benchmarks are done with 10 concurrent connections.
- SET key value + GET key
- redis-py: 11.76 Kops
- redis-py with hiredis-py: 13.40 Kops
- improvement: 1.1x
List entries in the following tests are 5 bytes.
- LRANGE list 0 9:
- redis-py: 4.78 Kops
- redis-py with hiredis-py: 12.94 Kops
- improvement: 2.7x
- LRANGE list 0 99:
- redis-py: 0.73 Kops
- redis-py with hiredis-py: 11.90 Kops
- improvement: 16.3x
- LRANGE list 0 999:
- redis-py: 0.07 Kops
- redis-py with hiredis-py: 5.83 Kops
- improvement: 83.2x
Throughput improvement for simple SET/GET is minimal, but the larger multi bulk replies
get, the larger the performance improvement is.
License
This code is released under the BSD license, after the license of hiredis.