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1 # -----------------------------------------------------------------------------
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2 # calc.py
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3 #
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4 # A calculator parser that makes use of closures. The function make_calculator()
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5 # returns a function that accepts an input string and returns a result. All
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6 # lexing rules, parsing rules, and internal state are held inside the function.
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7 # -----------------------------------------------------------------------------
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8
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9 import sys
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10 sys.path.insert(0,"../..")
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11
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12 if sys.version_info[0] >= 3:
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13 raw_input = input
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14
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15 # Make a calculator function
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16
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17 def make_calculator():
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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
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21 # ------- Internal calculator state
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22
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23 variables = { } # Dictionary of stored variables
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24
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25 # ------- Calculator tokenizing rules
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26
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27 tokens = (
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28 'NAME','NUMBER',
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29 )
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30
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31 literals = ['=','+','-','*','/', '(',')']
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32
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33 t_ignore = " \t"
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34
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35 t_NAME = r'[a-zA-Z_][a-zA-Z0-9_]*'
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36
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37 def t_NUMBER(t):
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38 r'\d+'
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39 t.value = int(t.value)
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40 return t
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41
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42 def t_newline(t):
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43 r'\n+'
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44 t.lexer.lineno += t.value.count("\n")
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45
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46 def t_error(t):
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47 print("Illegal character '%s'" % t.value[0])
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48 t.lexer.skip(1)
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49
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50 # Build the lexer
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51 lexer = lex.lex()
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52
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53 # ------- Calculator parsing rules
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54
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55 precedence = (
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56 ('left','+','-'),
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57 ('left','*','/'),
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58 ('right','UMINUS'),
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59 )
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60
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61 def p_statement_assign(p):
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62 'statement : NAME "=" expression'
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63 variables[p[1]] = p[3]
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64 p[0] = None
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65
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66 def p_statement_expr(p):
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67 'statement : expression'
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68 p[0] = p[1]
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69
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70 def p_expression_binop(p):
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71 '''expression : expression '+' expression
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72 | expression '-' expression
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73 | expression '*' expression
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74 | expression '/' expression'''
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75 if p[2] == '+' : p[0] = p[1] + p[3]
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76 elif p[2] == '-': p[0] = p[1] - p[3]
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77 elif p[2] == '*': p[0] = p[1] * p[3]
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78 elif p[2] == '/': p[0] = p[1] / p[3]
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79
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80 def p_expression_uminus(p):
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81 "expression : '-' expression %prec UMINUS"
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82 p[0] = -p[2]
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83
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84 def p_expression_group(p):
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85 "expression : '(' expression ')'"
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86 p[0] = p[2]
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87
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88 def p_expression_number(p):
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89 "expression : NUMBER"
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90 p[0] = p[1]
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91
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92 def p_expression_name(p):
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93 "expression : NAME"
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94 try:
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95 p[0] = variables[p[1]]
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96 except LookupError:
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97 print("Undefined name '%s'" % p[1])
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98 p[0] = 0
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99
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100 def p_error(p):
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101 if p:
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102 print("Syntax error at '%s'" % p.value)
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103 else:
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104 print("Syntax error at EOF")
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105
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106
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107 # Build the parser
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108 parser = yacc.yacc()
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109
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110 # ------- Input function
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111
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112 def input(text):
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113 result = parser.parse(text,lexer=lexer)
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114 return result
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115
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116 return input
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117
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118 # Make a calculator object and use it
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119 calc = make_calculator()
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120
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121 while True:
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122 try:
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123 s = raw_input("calc > ")
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124 except EOFError:
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125 break
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126 r = calc(s)
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127 if r:
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128 print(r)
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129
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130
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