More error checking in MixedIntegerLinearProgram

[mkoeppe]

The get_values method silently ignored non-variables.

[mkoeppe]

The get_values method silently ignored non-variables.

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New commits:

​dc3895b

MixedIntegerLinearProgram.get_values: Input checking

[vdelecroix]

Please use new style error ValueError(msg) instead of ValueError, msg (Python 3 compatibility).

Would be better to use repr rather than str. The output of "{!r}".format(l) is nicer than str(l). As you can see

sage: l = 1
sage: str(l)
'1'
sage: "{!r}".format(l)
'1'
sage: l = '1'
sage: str(l)
'1'
sage: "{!r}".format(l)
"'1'"

The following are not caught correctly

sage: M1 = MixedIntegerLinearProgram()
sage: M2 = MixedIntegerLinearProgram()
sage: x = M1.new_variable()
sage: y = M1.new_variable()
sage: z = M2.new_variable()
sage: M2.add_constraint(z[0] <= 5)
sage: M2.solve()
0.0
sage: M2.get_values(x)              # should be a ValueError
Traceback (most recent call last):
...
KeyError: x_0
sage: M2.get_values(y)              # should be a ValueError
{}

[vdelecroix]

And if the input is not a variable it would be better to raise a TypeError rather than a ValueError.

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​4290bde

MixedIntegerLinearProgram: use new style error ValueError(msg) instead of ValueError, msg (Python 3 compatibility).

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​67a263d	MIPVariable: New method mip
​13e82d9	MixedIntegerLinearProgram.get_values: Also check that a MIPVariable is from the right MIP

[vdelecroix]

Nice.

Last thing: the first error should be a ValueError. The type is indeed the good one!

[mkoeppe]

Should I then make it a ValueError also when it's a string, but not one that names a variable? (If so, what's the right way to test if it is a string?)

[vdelecroix]

Replying to mkoeppe:

Should I then make it a ValueError also when it's a string, but not one that names a variable? (If so, what's the right way to test if it is a string?)

Not necessarily (one can assume that the "good" way of calling this function is with a MIP variable). Though, to test if the object x is a string you can use isinstance(x, str) (which returns a boolean).

[mkoeppe]

I was confused, it actually does not accepts strings -- only MIPVariable objects.

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​7d7aeed

MixedIntegerLinearProgram.get_values: Raise TypeError when not a MIPVariable, ValueError when from the wrong MIP

[mkoeppe]

Thanks for reviewing!