What is the best way to implement this Python code

Question

I have this simple code here:

def myFunction(a: my_enumA, b: my_enumB, c: my_enumC):
  
  if a:
    update_a = update_from_db_a(a=a)
  else:
    update_a = True
  
  if b:
    update_b = update_from_db_b(b=b)
  else:
    update_b = True
  
  if c:
    update_c = update_from_db_c(c=c)
  else:
    update_c = True
    
  if update_a and update_b and update_c:
    return True
  else:
    return False

I'm sure that a design patern exists for this but I don't know the name.

What is the best way Pythonic way to implement it ? Maybe with a design pattern?

Isn't that equivalent to just returning not(a or b or c) ? What do the update_from_db_X return ? — Mateo Vial
– Mateo Vial, Commented Mar 7, 2022 at 14:21
I question the need for this kind of wrapper function in the first place. Let the caller decide whether the appropriate update functions need to be called, then pass a list like [update_from_db_a(v1), True, update_from_db_c(v3)] to all. — chepner
– chepner, Commented Mar 7, 2022 at 14:22
That was my first idea. update_from_db must be done to save some data in the database. In your example, if b is false, it won't try to save the data for c. — Langouste
– Langouste, Commented Mar 7, 2022 at 14:23
The function update make a query to save some data and return Trueif it works or False if it does not work — Langouste
– Langouste, Commented Mar 7, 2022 at 14:45

aaossa · Accepted Answer · 2022-03-07 14:25:48Z

3

You could transform each of your first ifs into a single statement:

# If a is False, value is True
# If a is True, value is update_from_db_a(a=a)
update_a = not a or update_from_db_a(a=a)

Notice that if not a is True (a.k.a a is False) it won't execute the next part of the condition (it won't call update_from_db_a).

Also, your function will return True only if a condition is True, so you could re-write it like this:

# If condition is True, returns True
# If condition is False, returns False
return update_a and update_b and update_c

Resulting code:

def myFunction(a: my_enumA, b: my_enumB, c: my_enumC):
    update_a = not a or update_from_db_a(a=a)
    update_b = not b or update_from_db_b(b=b)
    update_c = not c or update_from_db_c(c=c)
    return update_a and update_b and update_c

edited Mar 7, 2022 at 14:25

answered Mar 7, 2022 at 14:19

aaossa

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1 Comment

Langouste Over a year ago

"Also, your function will return True only if a condition is True, so you could re-write it like this:" No I can't. I need to go to update_from_db_a, if a = True but also if in update_from_db_b if b = true

score 1 · Accepted Answer · 2022-03-07 14:32:04Z

1

You can compress all conditions and pass them to all():

def myFunction(a: my_enumA, b: my_enumB, c: my_enumC):
    return all([
        not a or update_from_db_a(a=a),
        not b or update_from_db_b(b=b),
        not c or update_from_db_c(c=c)
    ])

Be sure to wrap them in an iterable, such as a list, tuple or set, and not in a generator. Otherwise all() will terminate on the first false condition.

edited Mar 7, 2022 at 14:32

answered Mar 7, 2022 at 14:25

user3515670

2 Comments

aaossa Over a year ago

Why a set in particular? I think a tuple or list would do the job too. The important part is to avoid using a generator right?

user3515670 Over a year ago

Right. I chose a set out of habit, because on large sets of conditions it only stores one instance of True or False and might accelerate all(). But you can also use a tuple or a list.

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