"Tips" Python implementation list deduction for function return values

Background

Imagine a scenario where we define the function foo to generate a random code greater than 0. However, the function execution may have an exception, and for the exception we specify that the function returns-1.

In the case of batch processing, we want to get a collection of the return values of all successfully executed Foo functions, ignoring the case of return-1. The basic logic is as follows:

result = [] for in item_lst:    = foo (item)    if code! =-1 :        result.append (code)

Solutions for using list derivation

If you want to implement it in the form of a list deduction, there are several solutions:

Solution 1:

 for inch  forif code! =-1]

The return value of the function is obtained by using a list deduction, and then the filter is performed, and a two-time list deduction is required.

Solution 2:

 for inch if foo (item)! =-1]

Performs a list deduction once, but it is clear that the Foo function was executed two times. It can be problematic if the Foo function is time-consuming, or if multiple executions can have side effects.

Solution 3:

 for inch  for inch if Code! =-1]

Using a generator expression to handle intermediate results, without a temporary list, and based on iterators, is preferable to both methods.

Reference

1. How to execute a filter by function return value in list comprehension?

"Tips" Python implementation list deduction for function return values