What is the preferred way to iterate through a list of items created on the fly?

Question

Basically, I have some variables and I want to quickly iterate through it.

I see three possibilities:

Using a list
Using a tuple
Using an implicit tuple

Respectively for example:

for regex in [regex_mail, regex_name]:
    ...

for regex in (regex_mail, regex_name):
    ...

for regex in regex_mail, regex_name:
    ...

Is there any reference indicating the syntax I should to use?
I looked at PEP8 but nothing is said about it.

I know this question may look as "primarily opinion based", but I am looking for concrete arguments that might allow me to choose the most adapted style (and PEP20 states that "There should be preferably only one way to do it").

The second and third examples shown are exactly the same. The parentheses are only needed with a tuple on occasions where precedence demands it. The comma makes the tuple, not the brackets. Generally a tuple is more efficient than a list. — cdarke, Sep 09 '17 at 19:00
Possible duplicate: https://stackoverflow.com/questions/6000291/best-style-for-iterating-over-a-small-number-of-items-in-python — andyhasit, Sep 09 '17 at 19:09
My 2 cents: it doesn't matter very much. But the desire to iterate over named variables is often a code smell: it indicates that the data might belong in a collection data structure (or iterable object) that is given a meaningful name, rather than in atomic variables. — FMc, Sep 09 '17 at 19:12
Opinion: Ignore any micro-benchmarks, and use a list because the value is *conceptually* a list; it is homogeneous and its cardinality is not fundamentally important. I often find it's helpful to imagine a statically typed language for comparison - in Haskell you'd write this with a list as `traverse_ (\regex -> ...) [regex_mail, regex_name]` (and it'd take some effort with generics or lenses to do the same with a tuple). — Chris Martin, Sep 09 '17 at 21:02

score 2 · Accepted Answer · answered Sep 09 '17 at 21:06

First, any performance difference between the 3 syntaxes is probably negligible.

Then, this answer does a good job at describing the difference between lists and tuples:

Tuples are heterogeneous data structures (i.e., their entries have different meanings), while lists are homogeneous sequences. Tuples have structure, lists have order.

The usual example is a collection of GPS coordinates. Use a tuple to separate X, Y and Z, use a list to separate coordinates :

[(48.77, 9.18, 400), (48.77, 9.185, 405), (48.77, 9.19, 410)]

According to this philosophy, a list should be used in your case.

What is the preferred way to iterate through a list of items created on the fly?

1 Answers1