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comparison ply-3.8/example/calceof/calc.py @ 7267:343ff337a19b

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<ais523> ` tar -xf ply-3.8.tar.gz
author HackBot
date Wed, 23 Mar 2016 02:40:16 +0000
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7266:61a39a120dee 7267:343ff337a19b
1 # -----------------------------------------------------------------------------
2 # calc.py
3 #
4 # A simple calculator with variables. Asks the user for more input and
5 # demonstrates the use of the t_eof() rule.
6 # -----------------------------------------------------------------------------
7
8 import sys
9 sys.path.insert(0,"../..")
10
11 if sys.version_info[0] >= 3:
12 raw_input = input
13
14 tokens = (
15 'NAME','NUMBER',
16 )
17
18 literals = ['=','+','-','*','/', '(',')']
19
20 # Tokens
21
22 t_NAME = r'[a-zA-Z_][a-zA-Z0-9_]*'
23
24 def t_NUMBER(t):
25 r'\d+'
26 t.value = int(t.value)
27 return t
28
29 t_ignore = " \t"
30
31 def t_newline(t):
32 r'\n+'
33 t.lexer.lineno += t.value.count("\n")
34
35 def t_eof(t):
36 more = raw_input('... ')
37 if more:
38 t.lexer.input(more + '\n')
39 return t.lexer.token()
40 else:
41 return None
42
43 def t_error(t):
44 print("Illegal character '%s'" % t.value[0])
45 t.lexer.skip(1)
46
47 # Build the lexer
48 import ply.lex as lex
49 lex.lex()
50
51 # Parsing rules
52
53 precedence = (
54 ('left','+','-'),
55 ('left','*','/'),
56 ('right','UMINUS'),
57 )
58
59 # dictionary of names
60 names = { }
61
62 def p_statement_assign(p):
63 'statement : NAME "=" expression'
64 names[p[1]] = p[3]
65
66 def p_statement_expr(p):
67 'statement : expression'
68 print(p[1])
69
70 def p_expression_binop(p):
71 '''expression : expression '+' expression
72 | expression '-' expression
73 | expression '*' expression
74 | expression '/' expression'''
75 if p[2] == '+' : p[0] = p[1] + p[3]
76 elif p[2] == '-': p[0] = p[1] - p[3]
77 elif p[2] == '*': p[0] = p[1] * p[3]
78 elif p[2] == '/': p[0] = p[1] / p[3]
79
80 def p_expression_uminus(p):
81 "expression : '-' expression %prec UMINUS"
82 p[0] = -p[2]
83
84 def p_expression_group(p):
85 "expression : '(' expression ')'"
86 p[0] = p[2]
87
88 def p_expression_number(p):
89 "expression : NUMBER"
90 p[0] = p[1]
91
92 def p_expression_name(p):
93 "expression : NAME"
94 try:
95 p[0] = names[p[1]]
96 except LookupError:
97 print("Undefined name '%s'" % p[1])
98 p[0] = 0
99
100 def p_error(p):
101 if p:
102 print("Syntax error at '%s'" % p.value)
103 else:
104 print("Syntax error at EOF")
105
106 import ply.yacc as yacc
107 yacc.yacc()
108
109 while 1:
110 try:
111 s = raw_input('calc > ')
112 except EOFError:
113 break
114 if not s: continue
115 yacc.parse(s+'\n')