4. Code standard

  • Code at least should work under python-2.7, gcc-4.8.

  • 90/10 functional/OOP, unless performance critical, functions are pure.

  • 90/10 Python/C, only computational hot spots were written in C.

  • To extend python function with C/Fortran:

  • Conservative on advanced language feature.

  • Minimal dependence principle

    • Minimal requirements on 3rd party program or libraries.

    • Loose-coupling between modules so that the failure of one module can have minimal effects on the other modules.

  • Not enforced but recommended - Compatible with Python 2.6, 2.7, 3.2, 3.3, 3.4; - Following C89 (gnu89) standard for C code; - Using ctypes to bridge C/python functions

4.1. Name convention

  • The prefix or suffix underscore in the function names have special meanings

    • functions with prefix-underscore like _fn are private functions. They are typically not documented, and not recommended to use.

    • functions with suffix-underscore like fn_ means that they have side effects. The side effects include the change of the input argument, the runtime modification of the class definitions (attributes or members), or module definitions (global variables or functions) etc.

    • regular (pure) functions do not have underscore as the prefix or suffix.

4.2. API convention

  • gto.Mole holds all global parameters, like the log level, the max memory usage etc. They are used as the default value for all other classes.

  • Method class.

    • Most QC method classes (like HF, CASSCF, FCI, …) directly take three attributes verbose, stdout and max_memory from gto.Mole. Overwriting them only affects the behavior of the local instance for that method class. In the following example, mf.verbose mutes the noises produced by RHF method, and the output of MP2 is written in the log file example.log:

      >>> from pyscf import gto, scf, mp
      >>> mol = gto.M(atom='H 0 0 0; H 0 0 1', verbose=5)
      >>> mf = scf.RHF(mol)
      >>> mf.verbose = 0
      >>> mf.kernel()
      >>> mp2 = mp.MP2(mf)
      >>> mp2.stdout = open('example.log', 'w')
      >>> mp2.kernel()
    • Method class are only to hold the options or environments (like convergence threshold, max iterations, …) to control the behavior/convergence of the method. The intermediate status are not supposed to be saved in the method class (during the computation). However, the final results or solutions are kept in the method object for convenience. Once the results are stored in the particular method class, they are assumed to be read only, since many class member functions take them as the default arguments if the caller didn’t provide enough parameters.

    • In __init__ function, initialize/define the problem size. The problem size parameters (like num_orbitals etc) can be considered as environments. They are not supposed to be changed by other functions.

    • Kernel functions Although the method classes have various entrance/main function, many of them provide an entrance function called kernel. You can simply call the kernel function and it will guide the program flow to the right main function.

    • Default value of class methods’ arguments. Many class methods can take the results of the calculations which were held in the class as the default arguments.

  • Function arguments

    • First argument is handler. The handler is one of gto.Mole object, a mean-field object, or a post-Hartree-Fock object.