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7267
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1 #!/usr/bin/env python
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2
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3 # -----------------------------------------------------------------------------
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4 # calc.py
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5 #
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6 # A simple calculator with variables. This is from O'Reilly's
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7 # "Lex and Yacc", p. 63.
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8 #
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9 # Class-based example contributed to PLY by David McNab
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10 # -----------------------------------------------------------------------------
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11
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12 import sys
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13 sys.path.insert(0,"../..")
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14
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15 if sys.version_info[0] >= 3:
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16 raw_input = input
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17
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18 import ply.lex as lex
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19 import ply.yacc as yacc
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20 import os
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21
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22 class Parser:
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23 """
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24 Base class for a lexer/parser that has the rules defined as methods
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25 """
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26 tokens = ()
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27 precedence = ()
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28
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29 def __init__(self, **kw):
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30 self.debug = kw.get('debug', 0)
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31 self.names = { }
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32 try:
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33 modname = os.path.split(os.path.splitext(__file__)[0])[1] + "_" + self.__class__.__name__
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34 except:
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35 modname = "parser"+"_"+self.__class__.__name__
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36 self.debugfile = modname + ".dbg"
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37 self.tabmodule = modname + "_" + "parsetab"
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38 #print self.debugfile, self.tabmodule
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39
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40 # Build the lexer and parser
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41 lex.lex(module=self, debug=self.debug)
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42 yacc.yacc(module=self,
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43 debug=self.debug,
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44 debugfile=self.debugfile,
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45 tabmodule=self.tabmodule)
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46
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47 def run(self):
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48 while 1:
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49 try:
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50 s = raw_input('calc > ')
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51 except EOFError:
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52 break
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53 if not s: continue
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54 yacc.parse(s)
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55
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56
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57 class Calc(Parser):
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58
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59 tokens = (
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60 'NAME','NUMBER',
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61 'PLUS','MINUS','EXP', 'TIMES','DIVIDE','EQUALS',
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62 'LPAREN','RPAREN',
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63 )
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64
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65 # Tokens
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66
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67 t_PLUS = r'\+'
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68 t_MINUS = r'-'
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69 t_EXP = r'\*\*'
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70 t_TIMES = r'\*'
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71 t_DIVIDE = r'/'
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72 t_EQUALS = r'='
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73 t_LPAREN = r'\('
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74 t_RPAREN = r'\)'
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75 t_NAME = r'[a-zA-Z_][a-zA-Z0-9_]*'
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76
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77 def t_NUMBER(self, t):
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78 r'\d+'
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79 try:
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80 t.value = int(t.value)
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81 except ValueError:
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82 print("Integer value too large %s" % t.value)
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83 t.value = 0
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84 #print "parsed number %s" % repr(t.value)
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85 return t
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86
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87 t_ignore = " \t"
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88
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89 def t_newline(self, t):
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90 r'\n+'
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91 t.lexer.lineno += t.value.count("\n")
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92
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93 def t_error(self, t):
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94 print("Illegal character '%s'" % t.value[0])
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95 t.lexer.skip(1)
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96
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97 # Parsing rules
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98
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99 precedence = (
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100 ('left','PLUS','MINUS'),
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101 ('left','TIMES','DIVIDE'),
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102 ('left', 'EXP'),
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103 ('right','UMINUS'),
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104 )
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105
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106 def p_statement_assign(self, p):
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107 'statement : NAME EQUALS expression'
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108 self.names[p[1]] = p[3]
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109
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110 def p_statement_expr(self, p):
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111 'statement : expression'
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112 print(p[1])
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113
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114 def p_expression_binop(self, p):
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115 """
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116 expression : expression PLUS expression
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117 | expression MINUS expression
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118 | expression TIMES expression
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119 | expression DIVIDE expression
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120 | expression EXP expression
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121 """
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122 #print [repr(p[i]) for i in range(0,4)]
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123 if p[2] == '+' : p[0] = p[1] + p[3]
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124 elif p[2] == '-': p[0] = p[1] - p[3]
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125 elif p[2] == '*': p[0] = p[1] * p[3]
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126 elif p[2] == '/': p[0] = p[1] / p[3]
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127 elif p[2] == '**': p[0] = p[1] ** p[3]
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128
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129 def p_expression_uminus(self, p):
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130 'expression : MINUS expression %prec UMINUS'
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131 p[0] = -p[2]
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132
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133 def p_expression_group(self, p):
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134 'expression : LPAREN expression RPAREN'
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135 p[0] = p[2]
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136
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137 def p_expression_number(self, p):
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138 'expression : NUMBER'
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139 p[0] = p[1]
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140
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141 def p_expression_name(self, p):
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142 'expression : NAME'
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143 try:
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144 p[0] = self.names[p[1]]
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145 except LookupError:
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146 print("Undefined name '%s'" % p[1])
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147 p[0] = 0
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148
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149 def p_error(self, p):
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150 if p:
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151 print("Syntax error at '%s'" % p.value)
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152 else:
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153 print("Syntax error at EOF")
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154
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155 if __name__ == '__main__':
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156 calc = Calc()
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157 calc.run()
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