Speedup of __add_triple_context

[rchateauneu]

Test parsing orkg.nt.

__add_triple_context needs to know if a triple was already inserted. The idea of this speed-up is to:

• avoid a triple lookup in the dictionary __spo,
• avoid a KeyError exception, because Python exceptions are expensive.
• If the triple was already inserted, do not insert it a second time in __pos and __osp.

Before:

After:

[coveralls]

Coverage increased (+0.008%) to 75.713% when pulling fec72c9 on rchateauneu:speedup_add_triple_context into 58b23fd on RDFLib:master.

[coveralls]

Coverage decreased (-0.0002%) to 75.705% when pulling fec72c9 on rchateauneu:speedup_add_triple_context into 58b23fd on RDFLib:master.