def _get_opstr(op, cls):
<EOL>subtyp = getattr(cls, '<STR_LIT>', '<STR_LIT>')<EOL>use_numexpr = '<STR_LIT>' not in subtyp<EOL>if not use_numexpr:<EOL><INDENT>return None<EOL><DEDENT>return {operator.add: '<STR_LIT:+>',<EOL>radd: '<STR_LIT:+>',<EOL>operator.mul: '<STR_LIT:*>',<EOL>rmul: '<STR_LIT:*>',<EOL>operator.sub: '<STR_LIT:->',<EOL>rsub: '<STR_LIT:->',<EOL>operator.truediv: '<STR_LIT:/>',<EOL>rtruediv: '<STR_LIT:/>',<EOL>operator.floordiv: '<STR_LIT>',<EOL>rfloordiv: '<STR_LIT>',<EOL>operator.mod: None,  <EOL>rmod: '<STR_LIT:%>',<EOL>operator.pow: '<STR_LIT>',<EOL>rpow: '<STR_LIT>',<EOL>operator.eq: '<STR_LIT>',<EOL>operator.ne: '<STR_LIT>',<EOL>operator.le: '<STR_LIT>',<EOL>operator.lt: '<STR_LIT:<>',<EOL>operator.ge: '<STR_LIT>',<EOL>operator.gt: '<STR_LIT:>>',<EOL>operator.and_: '<STR_LIT:&>',<EOL>rand_: '<STR_LIT:&>',<EOL>operator.or_: '<STR_LIT:|>',<EOL>ror_: '<STR_LIT:|>',<EOL>operator.xor: '<STR_LIT>',<EOL>rxor: '<STR_LIT>',<EOL>divmod: None,<EOL>rdivmod: None}[op]<EOL>
Find the operation string, if any, to pass to numexpr for this
operation.

Parameters
----------
op : binary operator
cls : class

Returns
-------
op_str : string or None