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Hi, I have a project called "astoptimizer" which does the same job than the CPython peephole optimizer, but it is implemented in Python.
To avoid this issue (create an huge object and then discard it because it is too large), I have a "check_binop_cst" function which checks if the result will fit into the configuration constraints:
https://bitbucket.org/haypo/astoptimizer/src/024c05ae410458813c20fafe8fe5b8d3cf980f52/astoptimizer/optimizer.py?at=default#cl-598
Check for "a * b" :
-------------
 if isinstance(op, ast.Mult):
 if isinstance(right, INT_TYPES):
 # str * int
 if isinstance(left, STR_TYPES):
 return (len(left) * right <= self.config.max_string_length)
 # tuple * int
 if isinstance(left, tuple):
 return (len(left) * right <= self.config.max_tuple_length)
 if isinstance(left, INT_TYPES):
 # int * str
 if isinstance(right, STR_TYPES):
 return (left * len(right) <= self.config.max_string_length)
 # int * tuple
 if isinstance(right, tuple):
 return (left * len(right) <= self.config.max_tuple_length)
-------------
Constraints in the config:
https://bitbucket.org/haypo/astoptimizer/src/024c05ae410458813c20fafe8fe5b8d3cf980f52/astoptimizer/config.py?at=default#cl-187
Astoptimizer supports the following "constant" types: int, float, complex, bytes, str, tuple, "name constant" (True, False, None). The frozenset type is also supported if the builtins are declared as "cosntant" too.