DOC-5225 started probabilistic examples page for Python

Author: andy-stark-redis

content/develop/clients/redis-py/prob.md

@@ -0,0 +1,60 @@
+---
+categories:
+- docs
+- develop
+- stack
+- oss
+- rs
+- rc
+- oss
+- kubernetes
+- clients
+description: Learn how to use approximate statistics with Redis.
+linkTitle: Probabilistic data types
+title: Probabilistic data types
+weight: 45
+---
+
+Redis supports several
+[probabilistic data types]({{< relref "/develop/data-types/probabilistic" >}})
+that let you gather approximate statistical information. To see why
+this would be useful, consider the task of counting the number
+of distinct IP addresses that access a website in one day.
+
+Assuming that you already have code that supplies you with each IP
+address as a string, you could record the addresses in Redis using
+a [set]({{< relref "/develop/data-types/sets" >}}):
+
+```py
+r.sadd("ip_tracker", new_ip_address)
+```
+
+The set can only contain each key once, so if the same address
+appears again during the day, the new instance will not change
+the set. At the end of the day, you could get the exact number of
+distinct addresses using the `scard()` function:
+
+```py
+num_distinct_ips = r.scard("ip_tracker")
+```
+
+This approach is simple, effective, and precise but if your website
+is very busy, the `ip_tracker` set could become very large and consume
+a lot of memory.
+
+The count of distinct IP addresses would probably be rounded to the
+nearest thousand or more when the usage statistics are delivered, so
+getting it exactly right is not important. It would be useful
+if you could trade off some precision in exchange for lower memory
+consumption and obfuscation of IP address strings. The probabilistic
+data types provide exactly this kind of trade-off for statistics.
+Specifically, you can count the approximate number of items in a
+set using the
+[HyperLogLog]({{< relref "/develop/data-types/probabilistic/hyperloglogs" >}})
+data type, as described below.
+
+## HyperLogLog
+
+A HyperLogLog object works in a similar way to a [set]({{< relref "/develop/data-types/sets" >}}),
+except that it only lets you add items and approximate the number of items
+in the set (also known as the *cardinality* of the set).