Getting started with redis-py

This post explains how to interface with Redis from Python and how to use different Redis commands from Python using redis-py.

What this post is not about

• Comparing relational and non-relational database
• Comparing MySQL and Redis
• Introduction to Redis

I assume you know the following

• Basics of Redis
• Basic redis commands for working with Strings, Lists and Maps as described at Redis docs.

I did not find enough examples of using redis-py provided methods and so wrote this blog post.

Getting started

Assuming you have Redis installed and your redis server is running.

We will follow the same sequence as followed in Redis data-types-intro at Redis docs

Install redis-py

pip install redis

Start redis-cli on some shell, so we can relate our Python redis commands and plain redis command.

Redis strings

For setting a string value, we use the following from redis-cli

127.0.0.1:6379> set mykey myvalue

And you can get it using

127.0.0.1:6379> get mykey
"myvalue"

Now we want to do the same from Python. Do the following from Python shell.

>>> import redis
>>> r = redis.StrictRedis()

We created an instance of StrictRedis. This is required for communication with redis-server.

Try getting “mykey”, which was set using redis-cli, from Python

>>> r.get("mykey")
'myvalue'   #output

So we are able to communicate properly with redis-server. Things which were inserted into redis using redis-cli can be read using Python.

Try setting a value into Redis from Python shell.

>>> r.set("anotherkey", "anothervalue")
True       #output

Check from redis-cli if this key was set properly.

127.0.0.1:6379> get anotherkey
"anothervalue"

So it seems Python is able to insert values into Redis properly.

You can read the same value using Python again.

>>> r.get("anotherkey")
'anothervalue'

INCR and INCRBY

Redis provides incr and incrby on integer values.

So let’s set an integer value first which we will try to increment.

>>> r.set("num", 10)
True

>>> r.get("num")
'10'

redis-py’s equivalent of Redis’ incr is

>>> r.incr("num")
11

Get it to verify that num has been incremented

>>> r.get("num")
'11'

You should verify it using redis-cli too.

127.0.0.1:6379> get num
"11"

Python’s equivalent of incrby is

>>> r.incrby("num", 10)
21

Verify again using redis-cli

127.0.0.1:6379> get num
"21"

MSET and MGET

redis-cli’s mset equivalent in Python

>>> r.mset(first_num=1, second_num=2, third_num=3)
True

Verify these keys are set from redis-cli

127.0.0.1:6379> get first_num
"1"
127.0.0.1:6379> get second_num
"2"

reidis’ mget equivalent

>>> r.mget(["first_num", "second_num"])
['1', '2']

EXISTS

>>> r.exists("first_num")
True
>>> r.exists("fourth_num")
False

DEL

>>> r.delete("first_num")
1

As this key is deleted now, you will get “nil” and “None” if you try to retrieve it.

From redis-cli

127.0.0.1:6379> get first_num
(nil)

From Python shell

>>> r.get("first_num")

EXPIRE

Mark key second_num to expire after 10 seconds

>>> r.expire("second_num", 10)
True

Check this immediately

>>> r.get("second_num")
'2'     #output

Check after 10 seconds

>>> r.get("second_num")
It returns None after 10 seconds meaning this key doesn't exist in redis anymore

Redis Lists

reidis’ lpush equivalent in Python

>>> r.lpush("mylist", 1)
1L

Verify from redis-cli that a list is created in redis

127.0.0.1:6379> lrange mylist 0 -1
1) "1"

Pushing multiple values to list

>>> r.lpush("mylist", 2, 3)

Check the new list from redis-cli

127.0.0.1:6379> lrange mylist 0 -1
1) "3"
2) "2"
3) "1"

redis-cli’s lrange equivalent in Python

>>> r.lrange("mylist", 0, -1)
['3', '2', '1']

>>> r.lrange("mylist", 0, 1)
['3', '2']

rpush

>>> r.rpush("mylist", 4)

Check that element is pushed on right

>>> r.lrange("mylist", 0, -1)
['3', '2', '1', '4']

Redis hashes

hmset allows saving of dictionary as values. You should already be knowing this from redis docs.

127.0.0.1:6379> hmset user name ned age 31
OK

127.0.0.1:6379> hgetall user
1) "name"
2) "ned"
3) "age"
4) "31"

redis-py way of achieving the same would be

>>> r.hmset("another_user", {'name': 'robert', 'age': 32})
True

Try reading this using redis-cli

127.0.0.1:6379> hgetall another_user
1) "age"
2) "32"
3) "name"
4) "robert"

Try reading this using redis-py

>>> r.hgetall("another_user")
{'age': '32', 'name': 'robert'}

>>> r.hget("another_user", "name")
'robert'

>>> r.hget("another_user", "age")
'32'

>>> r.hgetall("user")
{'age': '31', 'name': 'ned'}

There are several other methods provided by redis-py too and now you should be in a good position to related redis’ commands with redis-py methods.

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