Python - define constant inside function

Question

Given that there are no real constants in Python, the convention is to name them in CAPS for conveying the intentions.

In following sample code, FIRST and SECOND are constants:

def fibonacci_generator(count):
    FIRST, SECOND = 0, 1
    a, b = FIRST, SECOND
    for _ in range(count):
        yield a
        a, b = b, a + b

print(list(fibonacci_generator(10)))

But for the two constants, PyCharm is giving warning as:

Variable in function should be lowercase

Is there any other correct way to define constants within functions? (Without suppressing the PyCharm warning)

Answer 1

According to PEP8 constants should be defined at the module level:

Constants are usually defined on a module level and written in all capital letters with underscores separating words. Examples include MAX_OVERFLOW and TOTAL.

There is no convention for naming constants inside functions or methods.

You can:

• Live with the warning, or
• Suppress it, or
• Use "normal" lowercase names

In this case, you could also use default arguments without getting a warning but it does seem like an overkill just to get around a PEP8 convention warning:

However, this is counter-productive because you violate one convention in order to not get a warning about violating another.

Answer 2

Besides what have been proposed by @DeepSpace, other potential choices are (1) using underscore-prefixed variable names such as _FIRST, _SECOND, etc.; (2) writing a class instead and make the constants class-level constants.