87b9f0b87b
In some newer Linux distributions, env python default to Python 3.0. This patch explicitly uses "python2" instead of just "python" for all scripts that use #! Reported-by: Sanchayan Maity <maitysanchayan@gmail.com> Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
160 lines
4 KiB
Python
Executable file
160 lines
4 KiB
Python
Executable file
#!/usr/bin/env python2
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# -----------------------------------------------------------------------------
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# calc.py
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#
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# A simple calculator with variables. This is from O'Reilly's
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# "Lex and Yacc", p. 63.
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#
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# Class-based example contributed to PLY by David McNab.
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#
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# Modified to use new-style classes. Test case.
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# -----------------------------------------------------------------------------
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import sys
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sys.path.insert(0,"../..")
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if sys.version_info[0] >= 3:
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raw_input = input
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import ply.lex as lex
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import ply.yacc as yacc
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import os
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class Parser(object):
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"""
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Base class for a lexer/parser that has the rules defined as methods
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"""
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tokens = ()
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precedence = ()
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def __init__(self, **kw):
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self.debug = kw.get('debug', 0)
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self.names = { }
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try:
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modname = os.path.split(os.path.splitext(__file__)[0])[1] + "_" + self.__class__.__name__
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except:
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modname = "parser"+"_"+self.__class__.__name__
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self.debugfile = modname + ".dbg"
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self.tabmodule = modname + "_" + "parsetab"
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#print self.debugfile, self.tabmodule
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# Build the lexer and parser
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lex.lex(module=self, debug=self.debug)
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yacc.yacc(module=self,
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debug=self.debug,
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debugfile=self.debugfile,
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tabmodule=self.tabmodule)
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def run(self):
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while 1:
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try:
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s = raw_input('calc > ')
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except EOFError:
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break
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if not s: continue
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yacc.parse(s)
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class Calc(Parser):
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tokens = (
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'NAME','NUMBER',
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'PLUS','MINUS','EXP', 'TIMES','DIVIDE','EQUALS',
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'LPAREN','RPAREN',
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)
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# Tokens
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t_PLUS = r'\+'
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t_MINUS = r'-'
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t_EXP = r'\*\*'
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t_TIMES = r'\*'
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t_DIVIDE = r'/'
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t_EQUALS = r'='
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t_LPAREN = r'\('
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t_RPAREN = r'\)'
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t_NAME = r'[a-zA-Z_][a-zA-Z0-9_]*'
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def t_NUMBER(self, t):
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r'\d+'
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try:
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t.value = int(t.value)
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except ValueError:
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print("Integer value too large %s" % t.value)
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t.value = 0
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#print "parsed number %s" % repr(t.value)
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return t
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t_ignore = " \t"
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def t_newline(self, t):
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r'\n+'
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t.lexer.lineno += t.value.count("\n")
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def t_error(self, t):
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print("Illegal character '%s'" % t.value[0])
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t.lexer.skip(1)
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# Parsing rules
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precedence = (
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('left','PLUS','MINUS'),
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('left','TIMES','DIVIDE'),
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('left', 'EXP'),
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('right','UMINUS'),
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)
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def p_statement_assign(self, p):
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'statement : NAME EQUALS expression'
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self.names[p[1]] = p[3]
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def p_statement_expr(self, p):
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'statement : expression'
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print(p[1])
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def p_expression_binop(self, p):
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"""
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expression : expression PLUS expression
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| expression MINUS expression
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| expression TIMES expression
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| expression DIVIDE expression
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| expression EXP expression
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"""
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#print [repr(p[i]) for i in range(0,4)]
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if p[2] == '+' : p[0] = p[1] + p[3]
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elif p[2] == '-': p[0] = p[1] - p[3]
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elif p[2] == '*': p[0] = p[1] * p[3]
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elif p[2] == '/': p[0] = p[1] / p[3]
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elif p[2] == '**': p[0] = p[1] ** p[3]
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def p_expression_uminus(self, p):
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'expression : MINUS expression %prec UMINUS'
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p[0] = -p[2]
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def p_expression_group(self, p):
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'expression : LPAREN expression RPAREN'
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p[0] = p[2]
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def p_expression_number(self, p):
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'expression : NUMBER'
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p[0] = p[1]
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def p_expression_name(self, p):
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'expression : NAME'
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try:
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p[0] = self.names[p[1]]
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except LookupError:
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print("Undefined name '%s'" % p[1])
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p[0] = 0
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def p_error(self, p):
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if p:
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print("Syntax error at '%s'" % p.value)
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else:
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print("Syntax error at EOF")
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if __name__ == '__main__':
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calc = Calc()
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calc.run()
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