Should I capitalize constant in Python?

Question

In PEP8, the general rule is to declare constants in UPPER_CASE chars. In real life, there can be a number of situations:

#!env python

DATABASE_HOST = 'localhost'
app = Flask('myapp')
base_two = partial(int, base=2) 

Typically we consider string-type or numeric-type variables as immutable and thus constants, but not object or function. The problem is there is no-way a linter can do type-checking.

How do you deal with this case? Should I capitalize them or just disable this rule in my linter?

Answer 1

Personally the only time I ever capitalise something is when providing a value externally that should never be changed. Otherwise, it's find to leave it in lowercase, especially if the value is just part of the logic flow. so

FLAG = object()

def func(arg_with_default = FLAG):
    if arg_with_default is FLAG:
         do_default()
    else:
         do_something_else(arg_with_default)

I think you're confusing immutability with constants.

t = (1, 2)
t[0] = 3  # error -- immutable
t = 3.14  # fine -- not constant

Python has no concept of constants. Every variable can be overridden, hence why in cases where it matters that a variable is not changed, that is perhaps the time to make that obvious by using capitalisation.

If the linter is complaining that you aren't capitalising things that don't need to be, I'd disable that option.