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POClass scope vs module scope attributes in Python
 

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  1. POClass scope vs module scope attributes in Python
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    <p>I declare a class that does some computations using several hard-coded constants that are defined as class attributes. All of the methods look similar to the following:</p> <pre><code>class IAPWS_1995: @staticmethod def dAr_ddelta(delta, tau, Delta, theta, psi): _dAr_ddelta = \ sum(IAPWS_1995.n_0 * IAPWS_1995.d_0 * pow(delta, IAPWS_1995.d_0-1) * pow(tau, IAPWS_1995.t_0)) + \ sum(IAPWS_1995.n_1 * exp(-pow(delta, IAPWS_1995.c_1)) * (pow(delta, IAPWS_1995.d_1-1) * pow(tau, IAPWS_1995.t_1) * (IAPWS_1995.d_1 - IAPWS_1995.c_1*pow(delta, IAPWS_1995.c_1)))) + \ sum(IAPWS_1995.n_2 * pow(delta, IAPWS_1995.d_2)*pow(tau, IAPWS_1995.t_2) * exp(-IAPWS_1995.alpha_2*(delta-IAPWS_1995.epsilon_2)**2 - IAPWS_1995.beta_2*(tau-IAPWS_1995.gamma_2)**2) * (IAPWS_1995.d_2/delta - 2*IAPWS_1995.alpha_2*(delta-IAPWS_1995.epsilon_2))) + \ sum(IAPWS_1995.n_3 * (pow(Delta, IAPWS_1995.b_3)*(psi + delta*IAPWS_1995.dpsi_ddelta(psi, delta)) + IAPWS_1995.dDeltab_ddelta(delta, Delta, theta)*delta*psi)) return _dAr_ddelta </code></pre> <p>The class scope qualifiers makes the code (even more) difficult to read. I had thought of doing something like this to make the code more readable:</p> <pre><code>... _ = IAPWS_1995 _dAr_ddelta = \ sum(_.n_0 * _.d_0 * pow(delta, _.d_0-1) * pow(tau, _.t_0)) + \ ... </code></pre> <p>If I move the constant declarations to the module scope, though, I don't need scope qualifiers at all. </p> <p>Is there a reason to prefer declaring the constants in the class over the module (e.g. namespace collisions if I have a similar class <code>IAPWS_2014</code> in the future?)</p>
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    1. COAre you using the class for anything other than grouping related constants together? Your function looks like it should be declared as a static method, as the first argument is not an instance of `IAPWD_1995`.
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    2. COThe class groups the related constants and functions together. Everything should be static--there is no state.
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    3. COSince your class has no instances, I think making it a module would make more sense. The constants would be module-level variables, and would be accessed as globals by the functions.
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