2 votes

Fortnightly Programming Q&A Thread

Automatically posted January 17, 2023

General Programming Q&A thread! Ask any questions about programming, answer the questions of other users, or post suggestions for future threads.

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Here is my schema:

```sql
CREATE TABLE article_to_warehouse (
  article_id   INTEGER
, warehouse_id INTEGER
)
;
```

How do I add a `UNIQUE` constraint?

3 comments

[3]
Bonooru
January 24, 2023 (edited January 24, 2023)
Link
I've got an algorithm that's in exponential time (ugh) and I can't seem to find a clever way around that. I've got a few optimizations that should let me abort early if there are bad combinations,...
I've got an algorithm that's in exponential time (ugh) and I can't seem to find a clever way around that. I've got a few optimizations that should let me abort early if there are bad combinations, but that's a separate issue. Anyone know a way to write for-loop chain that's depth is dependent on imported data in python?

I'm trying to avoid having to write nasty code like:
```
for aaa in [1,2,3]:
  for bbb in [1,2,3]:
    for ccc in [1,2,3]:
    ⋮
      for zzz in [1,2,3]:
        my_function(aaa,bbb,ccc, ... , zzz)
```
Especially since I don't know exactly how many members the for loop chain will have.

Thanks in advance!

EDIT:
The more I'm thinking about it, it should be trivial to calculate if I can generate every base-k number (where k is the number of options) of length n (where n is the length of my input). I think I can then write a function that takes that number as input, converts the numbers into the different choices and checks for optimizations and then runs my_function
3 votes
1. [2]
  onyxleopard
  January 24, 2023 (edited January 25, 2023)
  Link Parent
  I guess my first question is, for the values that you are iterating over in each loop, are they constant as in your example? If so, it seems like your innermost my_function could just be called on...
  
  I guess my first question is, for the values that you are iterating over in each loop, are they constant as in your example?
  
  If so, it seems like your innermost my_function could just be called on the product of [[1,2,3]] * depth (where depth is 24 in the case of aaa ... zzz). You could write this using itertools.product like so:
  
  from itertools import product arg_values = [1,2,3] depth = 3 args_list = list(product(*([arg_values] * depth))) # → [ # (1, 1, 1), # (1, 1, 2), # (1, 1, 3), # (1, 2, 1), # (1, 2, 2), # (1, 2, 3), # (1, 3, 1), # (1, 3, 2), # (1, 3, 3), # (2, 1, 1), # (2, 1, 2), # (2, 1, 3), # (2, 2, 1), # (2, 2, 2), # (2, 2, 3), # (2, 3, 1), # (2, 3, 2), # (2, 3, 3), # (3, 1, 1), # (3, 1, 2), # (3, 1, 3), # (3, 2, 1), # (3, 2, 2), # (3, 2, 3), # (3, 3, 1), # (3, 3, 2), # (3, 3, 3) # ] for args in args_list: my_function(*args)
  
  Edit:
  
  If you want to avoid allocating the list for the intermediate args_list, try consuming the generated args from product directly:
  
  for args in product(*([arg_values] * depth)): my_function(*args)
  
  3 votes
  1. Bonooru
    January 25, 2023
    Link Parent
    That will do the trick. I'd totally forgotten that itertools existed. Thanks for your help!
    
    That will do the trick. I'd totally forgotten that itertools existed. Thanks for your help!
    
    2 votes