Python: key = lambda usage explained in Sorted()

After a long long time, just documenting the usage of key = lambda anonymous function inside sorted()/sort() function.

Below is a beautiful explanation Posted by Paul G for a Python beginner lost in aspects of Python.

For the Python code:

mylist = [3,6,3,2,4,8,23]
sorted(mylist, key=lambda x: x%2==0)

[3, 3, 23, 6, 2, 4, 8] # Does this sorted result make intuitive sense to you?

Firstly, you'll notice that while the odds come before the evens, the evens themselves are not sorted. Why is this?? Lets read the docs:

Key Functions Starting with Python 2.4, both list.sort() and sorted() added a key parameter to specify a function to be called on each list element prior to making comparisons.

We have to do a little bit of reading between the lines here, but what this tells us is that the sort function is only called once, and if we specify the key argument, then we sort by the value that key function points us to.

What does the example using a modulo return? A boolean value: True=1, False=0. So how does sorted deal with this key? It bascially transforms the original list to a sequence of 1s and 0s.

[3,6,3,2,4,8,23] becomes [0,1,0,1,1,1,0]

Now we're getting somewhere. What do you get when you sort the transformed list?

[0,0,0,1,1,1,1]

Okay, so now we know why the odds come before the evens.

Link: https://stackoverflow.com/questions/8966538/syntax-behind-sortedkey-lambda

Practice Notes: Query for DAC metadata

Time and Again there may a situation where one may need find the DAC tasks which populate particular target table be it a temporary table or staging table or the warehouse table. This information could easily be found from the DAC interface. But if we need to get this data from a TOAD/SQL developer, the following query would do the work.

select step.name as "DAC TASK",

tbl.name as "TARGET TABLE",

step.app_wid as "ETL LAYER",

step.priority

from w_etl_step_tbl step_tbl,

w_etl_step step,

w_etl_table tbl

where tbl.row_wid = step_tbl.table_wid

and step.row_wid = step_tbl.step_wid

and tbl.name = 'W_EMPLOYEE_D'

and step_tbl.type_cd = 'Target'

order by step.priority, step.name

Practice Notes: PER_ALL_ASSINGMENTS_F ASSINGMENT_TYPE

Probably not worth blogging. But don't have mind to just leave it after having searched for quite sometime.

The lookup type for the PER_ALL_ASSINGMENTS_F.ASSINGMENT_TYPE is ALL_ASGN_TYPE

So next time i can just look at my diary.