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1 # -----------------------------------------------------------------------------
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2 # calc.py
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3 #
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4 # A simple calculator with variables. Asks the user for more input and
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5 # demonstrates the use of the t_eof() rule.
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6 # -----------------------------------------------------------------------------
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7
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8 import sys
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9 sys.path.insert(0,"../..")
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10
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11 if sys.version_info[0] >= 3:
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12 raw_input = input
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13
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14 tokens = (
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15 'NAME','NUMBER',
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16 )
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17
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18 literals = ['=','+','-','*','/', '(',')']
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19
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20 # Tokens
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21
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22 t_NAME = r'[a-zA-Z_][a-zA-Z0-9_]*'
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23
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24 def t_NUMBER(t):
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25 r'\d+'
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26 t.value = int(t.value)
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27 return t
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28
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29 t_ignore = " \t"
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30
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31 def t_newline(t):
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32 r'\n+'
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33 t.lexer.lineno += t.value.count("\n")
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34
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35 def t_eof(t):
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36 more = raw_input('... ')
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37 if more:
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38 t.lexer.input(more + '\n')
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39 return t.lexer.token()
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40 else:
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41 return None
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42
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43 def t_error(t):
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44 print("Illegal character '%s'" % t.value[0])
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45 t.lexer.skip(1)
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46
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47 # Build the lexer
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48 import ply.lex as lex
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49 lex.lex()
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50
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51 # Parsing rules
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52
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53 precedence = (
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54 ('left','+','-'),
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55 ('left','*','/'),
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56 ('right','UMINUS'),
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57 )
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58
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59 # dictionary of names
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60 names = { }
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61
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62 def p_statement_assign(p):
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63 'statement : NAME "=" expression'
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64 names[p[1]] = p[3]
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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 print(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] = names[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 import ply.yacc as yacc
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107 yacc.yacc()
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108
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109 while 1:
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110 try:
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111 s = raw_input('calc > ')
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112 except EOFError:
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113 break
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114 if not s: continue
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115 yacc.parse(s+'\n')
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