Need help to understand an one line code that extract subset dictionary with selected key and value pairs

I am working on a python project, I am creating a subset dictionary from the main dictionary, the subset dictionary only takes the key, value pairs that are under keys: ‘E’, ‘O’, ‘L’.

I found this code is working perfectly:

{key: self._the_main_dict[key] for key in self._the_main_dict.keys() & {'E', 'O', 'L'}}

However, I would like to understand how it works, can anyone please explain it in multiple lines of code, I guess it is something like: for key in ….

>Solution :

In short python has comprehensions that can provide one liner for datatype construction using for loops.

Here, this is an example of dictionary comprehension.

{key: self._the_main_dict[key] for key in self._the_main_dict.keys() & {'E', 'O', 'L'}}

This code can be extended to:

output = dict()
for key in self._the_main_dict.keys() & {'E', 'O', 'L'}:
  output[key] = self._the_main_dict[key]

output is the response provided by above dictionary comprehension.

self._the_main_dict.keys() & {'E', 'O', 'L'}. If you’re confused on this. This is just an Intersection operation between two sets. Yeah! Sets and Venn diagram you used to study in mathematics 😀