1  #!/usr/bin/env python3.8
       2  """Find the maximum amount of nesting for an expression that can be parsed
       3  without causing a parse error.
       4  
       5  Starting at the INITIAL_NESTING_DEPTH, an expression containing n parenthesis
       6  around a 0 is generated then tested with both the C and Python parsers. We
       7  continue incrementing the number of parenthesis by 10 until both parsers have
       8  failed. As soon as a single parser fails, we stop testing that parser.
       9  
      10  The grammar file, initial nesting size, and amount by which the nested size is
      11  incremented on each success can be controlled by changing the GRAMMAR_FILE,
      12  INITIAL_NESTING_DEPTH, or NESTED_INCR_AMT variables.
      13  
      14  Usage: python -m scripts.find_max_nesting
      15  """
      16  import sys
      17  import ast
      18  
      19  GRAMMAR_FILE = "data/python.gram"
      20  INITIAL_NESTING_DEPTH = 10
      21  NESTED_INCR_AMT = 10
      22  
      23  
      24  FAIL = "\033[91m"
      25  ENDC = "\033[0m"
      26  
      27  
      28  def check_nested_expr(nesting_depth: int) -> bool:
      29      expr = f"{'(' * nesting_depth}0{')' * nesting_depth}"
      30      try:
      31          ast.parse(expr)
      32          print(f"Nesting depth of {nesting_depth} is successful")
      33          return True
      34      except Exception as err:
      35          print(f"{FAIL}(Failed with nesting depth of {nesting_depth}{ENDC}")
      36          print(f"{FAIL}\t{err}{ENDC}")
      37          return False
      38  
      39  
      40  def main() -> None:
      41      print(f"Testing {GRAMMAR_FILE} starting at nesting depth of {INITIAL_NESTING_DEPTH}...")
      42  
      43      nesting_depth = INITIAL_NESTING_DEPTH
      44      succeeded = True
      45      while succeeded:
      46          expr = f"{'(' * nesting_depth}0{')' * nesting_depth}"
      47          if succeeded:
      48              succeeded = check_nested_expr(nesting_depth)
      49          nesting_depth += NESTED_INCR_AMT
      50  
      51      sys.exit(1)
      52  
      53  
      54  if __name__ == "__main__":
      55      main()