Dear all,
Many classes in SageMath (most of them? all of them? I don't know...)
have their attributes hidden by a leading `__`. Yet in Python hidden
attributes are never really hidden, since it is possible to access the
attribute `__hidden` of the class `MyClass` as `_MyClass__hidden`.
What SageMath's policy about using these hidden attributes in functions?
*A concrete example: *
For sparse polynomials (class `Polynomial_generic_sparse` in
`src/sage/rings/polynomial/polynomial_element_generic.py`), the
coefficients are stored as a dictionary, stored in the attribute
`__coeffs`. To compute the number of nonzero monomials, one can use any
of the following three solutions:
1. sage: len(p.coefficients()) # builds the list of (nonzero)
coefficients, and computes its length
2. sage: len(p.dict()) # copies the dictionary __coeffs and computes
its length
3. sage: len(p._Polynomial_generic_sparse__coeffs) # computes the
length of __coeffs
As one can expect, the fastest is solution 3. To get an idea of the
differences, with a random degree-10000 polynomial over ZZ, I get using
`timeit`:
1. 1.11 ms
2. 174 µs
3. 88 ns (with slowest run 46.05 times longer than fastest)
Thus if I implement a method `number_of_terms` in the class
`Polynomial_generic_sparse`, I am tempted to implement the third
solution. But is referring to a hidden attribute an issue?
Cheers,
Bruno
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