Pylint invalid constant name

Question

I'm receiving a Pylint error regarding my constant: MIN_SOIL_PARTICLE_DENS (invalid name). Any ideas why this constant is wrong? Here's my full function:

def bulk_density(clay, sand, organic_matter):
    MIN_SOIL_PARTICLE_DENS = 2.65
    x1 = (0.078 + 0.278 * sand + 0.034 * clay + 0.022 * organic_matter - 0.018
          * sand * organic_matter - 0.027 * clay * organic_matter - 0.584 * sand
          * clay)
    x2 = -0.107 + 1.636 * x1
    field_capacity = vol_water_content_33_j_kg(clay, sand, organic_matter)#m3/m3
    sat_water_content = 0.043 + field_capacity + x2 - 0.097 * sand
    return (1 - sat_water_content) * MIN_SOIL_PARTICLE_DENS

Answer 1

When checking names, Pylint differentiates between constants, variables, classes etc. Any name that is not inside a function/class will be considered a constant, anything else is a variable.

See http://docs.pylint.org/features.html#basic-checker

variable-rgx:
[a-z_][a-z0-9_]{2,30}$

const-rgx:
(([A-Z_][A-Z0-9_]*)|(__.*__))$

Because you're in a function, MIN_SOIL_PARTICLE_DENS is (according to pylint) supposed to be a variable, pylint however treats it as a constant and therefore complains.

This means you can't have any uppercase names inside functions without pylint complaining.

---

If you ask me, using uppercase inside functions is fine; not all constants are necessarily defined globally.

Answer 2

Few simple rules :

1. Constants should be defined with UPPER_CASE letters only and should be defined at the module level
2. Class names should be defined with CamelCase letters
3. Variables should be defined at lower_case and should be defined inside function, classes etc.

Now lets talk about your case,

MIN_SOIL_PARTICLE_DENS is defined inside a function and should have lower letters only. Thus instead of considering MIN_SOIL_PARTICLE_DENS as a constant, pylint considers it as a variable here and hence the pylint error.

Pylint Tutorial

Answer 3

I found this behavior annoying, but there's a way to configure pylint to avoid this!

Merge the following ini-style declaration into your .pylintrc file:

[BASIC]
variable-rgx=((([a-z_][a-z0-9_]{2,})|(_[a-z0-9_]*)|(__[a-z][a-z0-9_]+__))$)|([A-Z_][A-Z0-9_]+$)

I built this regex by taking

• the default snake_case regex taken from pylint's source at this line,

• the default CONST_VAR regex taken from pylint's source at this line

and joining them by | and some parentheses.

Theoretically, you could also just take .*, but this would allow even invalid names like mixed_CASE.