What is this python expression containing curly braces and a for in loop?
That's a dict comprehension.
It is just like a list comprehension
[3*x for x in range(5)]
--> [0,3,6,9,12]
except:
{x:(3*x) for x in range(5)}
---> { 0:0, 1:3, 2:6, 3:9, 4:12 }
- produces a Python
dictionary, not alist - uses curly braces
{}not square braces[] - defines key:value pairs based on the iteration through a list
In your case the keys are coming from the Code property of each element and the value is always set to empty array []
The code you posted:
order.messages = {c.Code:[] for c in child_orders}
is equivalent to this code:
order.messages = {}
for c in child_orders:
order.messages[c.Code] = []
See also:
- PEP0274
- Python Dictionary Comprehension
It's dictionary comprehension!
It's iterating through child_orders and creating a dictionary where the key is c.Code and the value is [].
More info here.