Adds Line2, Line3, SignalStats, Temperature python interface

[WagnerMarcos]

🎉 New feature

Goes on top of #216.

Related to #101 #210

Summary

Adds Python interface for three math classes: Line2, SignalStats, Temperature. For each class a python test has been created.

Related issues and notes

Line2

• Collinear() and Parallel() in ign-math was not working properly as the call to equal() was receiving (double, int, double) argument types, having a 0 with static cast passed as second argument, but always having doubles for the first and third arguments.. For this, a 0. is now being passed.
• Instead of copying using the assignment operator = in python for the tests, the copy constructor was used.
• To offer the operator[] functionality in python, the class had to be extended in the interface file (.i file) adding __getitem__(), calling the operator[] inside.
• To offer the serialization functionality in python, the class had to be extended in the interface file (.i file) adding __str__(), calling the operator<< inside.

Temperature

• To offer the serialization functionality in python, the class had to be extended in the interface file (.i file) adding __str__(), calling the operator<< inside.
• Setting a new temperature value with the assignment operator isn't possible in python, so the constructor is being called in the test where that was being used.
• The stream extraction operator hasn't been implemented in python to deserialize a string into an object.
• The friend Temperature operator+(double _t, const Temperature &_temp) and similar operators haven't been implemented in SWIG because no simple implementation was found. So it won't be possible to do temp1 = 20.0 + temp2.

SignalStats

This contains various classes defined in the same interface file.

SignalStats class

• A template for the map had to be created for it to be used as dictionaries in python.
• The copy constructor was used instead of the assignment operator in python tests.

SignalStatistic class and its inherited classes

• The copy functionality couldn't be done for the inherited classes, as the copy constructor was defined in the parent class, and in python it isn't assigning properly the class. A useful workaround in SWIG is yet to be found.

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

[codecov]

Codecov Report

Merging #220 (a905b63) into ign-math6 (23bcb08) will not change coverage.
The diff coverage is 100.00%.

❗ Current head a905b63 differs from pull request most recent head 8536f32. Consider uploading reports for the commit 8536f32 to get more accurate results

@@            Coverage Diff             @@
##           ign-math6     #220   +/-   ##
==========================================
  Coverage      99.21%   99.21%           
==========================================
  Files             65       65           
  Lines           6089     6089           
==========================================
  Hits            6041     6041           
  Misses            48       48           

Impacted Files	Coverage Δ
include/ignition/math/Line2.hh	100.00% <100.00%> (ø)

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[WagnerMarcos]

It was necessary to add the -Wno-class-memaccess flag to suppress the -Wclass-memaccess warning for the python target as when the std_map from SWIG is used with SWIG 3.0.12 in the SignalStats file, we were getting the following:

Click to see output

/ws/build/ignition-math6/lib/python/pythonPYTHON_wrap.cxx: In instantiation of 'static Type swig::traits_as<Type, swig::pointer_category>::as(PyObject*, bool) [with Type = std::pair<std::__cxx11::basic_string<char>, double>; PyObject = _object]':
/ws/build/ignition-math6/lib/python/pythonPYTHON_wrap.cxx:4153:64:   required from 'Type swig::as(PyObject*, bool) [with Type = std::pair<std::__cxx11::basic_string<char>, double>; PyObject = _object]'
/ws/build/ignition-math6/lib/python/pythonPYTHON_wrap.cxx:4720:20:   required from 'swig::SwigPySequence_Ref<T>::operator T() const [with T = std::pair<std::__cxx11::basic_string<char>, double>]'
/ws/build/ignition-math6/lib/python/pythonPYTHON_wrap.cxx:4780:14:   required from 'swig::SwigPySequence_ArrowProxy<T> swig::SwigPySequence_InputIterator<T, Reference>::operator->() const [with T = std::pair<std::__cxx11::basic_string<char>, double>; Reference = const swig::SwigPySequence_Ref<std::pair<std::__cxx11::basic_string<char>, double> >]'
/ws/build/ignition-math6/lib/python/pythonPYTHON_wrap.cxx:5464:25:   required from 'void swig::assign(const SwigPySeq&, std::map<K, T, Compare, Alloc>*) [with SwigPySeq = swig::SwigPySequence_Cont<std::pair<std::__cxx11::basic_string<char>, double> >; K = std::__cxx11::basic_string<char>; T = double; Compare = std::less<std::__cxx11::basic_string<char> >; Alloc = std::allocator<std::pair<const std::__cxx11::basic_string<char>, double> >]'
/ws/build/ignition-math6/lib/python/pythonPYTHON_wrap.cxx:5337:12:   required from 'static int swig::traits_asptr_stdseq<Seq, T>::asptr(PyObject*, swig::traits_asptr_stdseq<Seq, T>::sequence**) [with Seq = std::map<std::__cxx11::basic_string<char>, double>; T = std::pair<std::__cxx11::basic_string<char>, double>; PyObject = _object; swig::traits_asptr_stdseq<Seq, T>::sequence = std::map<std::__cxx11::basic_string<char>, double>]'
/ws/build/ignition-math6/lib/python/pythonPYTHON_wrap.cxx:5480:64:   required from 'static int swig::traits_asptr<std::map<_Key, _Tp, _Compare, _Allocator> >::asptr(PyObject*, swig::traits_asptr<std::map<_Key, _Tp, _Compare, _Allocator> >::map_type**) [with K = std::__cxx11::basic_string<char>; T = double; Compare = std::less<std::__cxx11::basic_string<char> >; Alloc = std::allocator<std::pair<const std::__cxx11::basic_string<char>, double> >; PyObject = _object; swig::traits_asptr<std::map<_Key, _Tp, _Compare, _Allocator> >::map_type = std::map<std::__cxx11::basic_string<char>, double>]'
/ws/build/ignition-math6/lib/python/pythonPYTHON_wrap.cxx:4045:37:   required from 'int swig::asptr(PyObject*, Type**) [with Type = std::map<std::__cxx11::basic_string<char>, double>; PyObject = _object]'
/ws/build/ignition-math6/lib/python/pythonPYTHON_wrap.cxx:34234:154:   required from here
/ws/build/ignition-math6/lib/python/pythonPYTHON_wrap.cxx:4128:8: warning: 'void* memset(void*, int, size_t)' clearing an object of type 'struct std::pair<std::__cxx11::basic_string<char>, double>' with no trivial copy-assignment; use assignment instead [-Wclass-memaccess]
  memset(v_def,0,sizeof(Type));
  ~~~~~~^~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/8/bits/stl_algobase.h:64,
                 from /usr/include/c++/8/bits/specfun.h:45,
                 from /usr/include/c++/8/cmath:1892,
                 from /usr/include/c++/8/math.h:36,
                 from /usr/include/python3.6m/pyport.h:194,
                 from /usr/include/python3.6m/Python.h:53,
                 from /ws/build/ignition-math6/lib/python/pythonPYTHON_wrap.cxx:173:
/usr/include/c++/8/bits/stl_pair.h:208:12: note: 'struct std::pair<std::__cxx11::basic_string<char>, double>' declared here
     struct pair
            ^~~~

This issue is not happening when compiling with SWIG 4.0, but in order to support SWIG 3.0, and as we couldn't find a fix for this at the moment, we decided to suppress it.

[francocipollone]

LGTM, just a couple of nits

[scpeters]

nit: can these be alphabetized or do they need to be ordered by dependencies?

[francocipollone]

do they need to be ordered by dependencies?

That's correct

[francocipollone]

LGTM!

@scpeters @chapulina It is ready for another review!