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  1. import pyparsing as pp
  2.  
  3. # works with and without packrat
  4. pp.ParserElement.enablePackrat()
  5.  
  6. pp.ParserElement.setDefaultWhitespaceChars(' \t')
  7.  
  8. operand = pp.Word(pp.nums)
  9. var = pp.Word(pp.alphas)
  10.  
  11. arith_expr = pp.Forward()
  12. arith_expr.ignore(pp.pythonStyleComment)
  13. lpar = pp.Suppress("(")
  14. rpar = pp.Suppress(")")
  15.  
  16. # code to implement selective ignore of NL's inside ()'s
  17. NL = pp.Suppress("\n")
  18. base_ignore = arith_expr.ignoreExprs[:]
  19. ignore_stack = base_ignore[:]
  20. def lpar_pa():
  21.     ignore_stack.append(NL)
  22.     arith_expr.ignore(NL)
  23.     #~ print('post-push', arith_expr.ignoreExprs)
  24. def rpar_pa():
  25.     ignore_stack.pop(-1)
  26.     arith_expr.ignore(None)
  27.     for e in ignore_stack:
  28.         arith_expr.ignore(e)
  29.     #~ print('post-pop', arith_expr.ignoreExprs)
  30. def reset_stack(*args):
  31.     arith_expr.ignore(None)
  32.     for e in base_ignore:
  33.         arith_expr.ignore(e)
  34.     #~ print('post-reset', arith_expr.ignoreExprs)
  35. lpar.addParseAction(lpar_pa)
  36. rpar.addParseAction(rpar_pa)
  37. arith_expr.setFailAction(reset_stack)
  38. arith_expr.addParseAction(reset_stack)
  39.  
  40. # now define the infix notation as usual
  41. arith_expr <<= pp.infixNotation(operand | var,
  42.     [
  43.     ("-", 1, pp.opAssoc.RIGHT),
  44.     (pp.oneOf("* /"), 2, pp.opAssoc.LEFT),
  45.     (pp.oneOf("- +"), 2, pp.opAssoc.LEFT),
  46.     ],
  47.     lpar=lpar, rpar=rpar
  48.     )
  49.  
  50. assignment = var + '=' + arith_expr
  51.  
  52. # Try it out!
  53. assignment.runTests([
  54. """a = 1 + 3""",
  55. """a = (1 + 3)""",
  56. """a = 1 + 2 + ( 
  57. 3 +
  58. 1)""",
  59. """a = 1 + 2 + (( 
  60. 3 +
  61. 1))""",
  62. """a = 1 + 2 +   
  63. 3""",
  64. """a = (1 + (2 + 3) +
  65. 4)""",
  66. ], fullDump=False)
Success #stdin #stdout 0.06s 13468KB
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Standard input is empty
stdout
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a = 1 + 3
FAIL-EXCEPTION: 'NoneType' object has no attribute 'copy'

a = (1 + 3)
FAIL-EXCEPTION: 'NoneType' object has no attribute 'copy'

a = 1 + 2 + ( 
3 +
1)
FAIL-EXCEPTION: 'NoneType' object has no attribute 'copy'

a = 1 + 2 + (( 
3 +
1))
FAIL-EXCEPTION: 'NoneType' object has no attribute 'copy'

a = 1 + 2 +   
3
FAIL-EXCEPTION: 'NoneType' object has no attribute 'copy'

a = (1 + (2 + 3) +
4)
FAIL-EXCEPTION: 'NoneType' object has no attribute 'copy'
https://ideone.com/NK9Y5y
language:
Python 3 (python  3.12)
created:
5 years ago
visibility:
public

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