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  1.  
  2. #Global variables
  3. ID_TOKEN = 1
  4. LPAREN_TOKEN = 2
  5. RPAREN_TOKEN = 3
  6. PLUS_OP_TOKEN = 4
  7. MULTI_OP_TOKEN = 5
  8. ILLEGAL_TOKEN = -1
  9. PARCOUNT = 0
  10. token = -1
  11. i = 0
  12. def scanner(user,length):
  13. 	global ID_TOKEN 
  14. 	global LPAREN_TOKEN 
  15. 	global RPAREN_TOKEN 
  16. 	global PLUS_OP_TOKEN 
  17. 	global MULTI_OP_TOKEN 
  18. 	global ILLEGAL_TOKEN
  19. 	if(i == length):
  20. 		return token
  21. 	elif (user[i] >= 'a' and user[i] <= 'z'):
  22. 		return  ID_TOKEN
  23. 	elif (user[i] == '('):
  24. 		return LPAREN_TOKEN
  25. 	elif (user[i] == ')'):
  26. 		return RPAREN_TOKEN
  27. 	elif (user[i] == '+'):
  28. 		return PLUS_OP_TOKEN
  29. 	elif (user[i] == '*'):
  30. 		return MULTI_OP_TOKEN
  31. 	elif(user[i] == '/0'):
  32. 		return END_TOKEN
  33. 	else:
  34. 		return ILLEGAL_TOKEN
  35.  
  36. def getNextChar():
  37. 	global i
  38. 	i = i+1
  39.  
  40. def expression(user,length):
  41. 	global ID_TOKEN 
  42. 	global LPAREN_TOKEN
  43. 	global RPAREN_TOKEN
  44. 	global PLUS_OP_TOKEN 
  45. 	global MULTI_OP_TOKEN 
  46. 	global ILLEGAL_TOKEN 
  47. 	global i
  48. 	global token
  49. 	global PARCOUNT
  50. 	if(token == ID_TOKEN):
  51. 		getNextChar()
  52. 		token = scanner(user,length)
  53. 		if(i == length):
  54. 			return True
  55. 		elif (token == MULTI_OP_TOKEN or token == PLUS_OP_TOKEN):
  56. 			getNextChar()
  57. 			token = scanner(user,length)
  58. 			return expression(user,length)
  59. 		elif(token  == RPAREN_TOKEN):
  60. 			if(PARCOUNT > 0):
  61. 				getNextChar()
  62. 				token = scanner(user,length)
  63. 				PARCOUNT = PARCOUNT -1
  64. 				if(PARCOUNT >0):
  65. 					return expression(user, length)
  66. 				elif(PARCOUNT == 0 and i == length):
  67. 					return True
  68. 			else:
  69. 				return False
  70. 	elif(token  == RPAREN_TOKEN and PARCOUNT >0):
  71. 		PARCOUNT = PARCOUNT -1
  72. 		if(PARCOUNT >0):
  73. 			getNextChar()
  74. 			token = scanner(user,length)
  75. 			return expression(user, length)
  76. 		elif(PARCOUNT == 0):
  77. 			return True
  78. 		else:
  79. 			return False
  80. 	elif(token == LPAREN_TOKEN):
  81. 		getNextChar()
  82. 		token = scanner(user,length)
  83. 		PARCOUNT = PARCOUNT + 1
  84. 		return expression(user,length)
  85. 	else:
  86. 		return False
  87.  
  88. def main():
  89. 	global ILLEGAL_TOKEN 
  90.  
  91. 	global token
  92. 	global i
  93. 	print("Hello! Welcome to Parser Function.")
  94. 	user = input("Please enter a string for parser to check: ")
  95. 	print("\n")	
  96. 	length = len(user)
  97. 	if(length > 0):
  98. 		token= scanner(user,length)
  99. 		if(token == ILLEGAL_TOKEN ):
  100. 			print(user, " is not an expression.")
  101. 		else:
  102. 			if(expression(user,length)):
  103. 				print(user, " is an expression.")
  104. 			else:
  105. 				print(user, "is not an expression.")
  106. 	elif (i == length):
  107. 			print( "This is not an expression.")
  108.  
  109. main()
Success #stdin #stdout 0.01s 28352KB
comments (?)
stdin
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z
(z)
a+b
(a+b)
a+b*z
a+(b*z)
a*(b+(c*d))
stdout
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Hello! Welcome to Parser Function.
Please enter a string for parser to check: 

z  is an expression.
https://ideone.com/9zbDJq
language:
Python 3 (python  3.9.5)
created:
7 years ago
visibility:
public

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