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161 ira 1 
#!/usr/bin/env python
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# Copyright: Ira W. Snyder
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# Start Date: 2005-11-18
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# End Date:
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# License: Public Domain
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#
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# Changelog Follows:
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#
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# 2005-11-18
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# * Just getting the basics in place, since we haven't been given
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#   the whole description of the project yet.
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#
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# Check for <Python-2.3 compatibility (boolean values)
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try:
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  True, False
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except NameError:
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  (True, False) = (1, 0)
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162 ira 20 
import sys
163 ira 21 
 
162 ira 22 
class RecursiveDescentParser:
161 ira 23 
    def __init__(self):
162 ira 24 
        self.__clear()
161 ira 25 
 
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    def __clear(self):
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        self.str = ""   # the string of input to test
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        self.strpos = 0 # the current position in str
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    def __input_test_str(self):
162 ira 31 
        self.str = raw_input("input str: ")
161 ira 32 
 
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    def main_menu(self):
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        done = False
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        while not done:
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            print 'Menu:'
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            print '========================================'
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            print '1. Test a string'
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            print '2. Quit'
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            print
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            s = raw_input('Choice >>> ')
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            print
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            if s == '1':
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                self.__clear()
161 ira 48 
                self.__input_test_str()
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                self.__test_str()
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            elif s == '2':
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                done = True
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            else:
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                print 'Bad Selection'
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                print
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162 ira 56 
    def __test_str(self):
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        print 'Parsing: %s' % (self.procE() and 'Completed' or 'Failed', )
163 ira 58 
        print
161 ira 59 
 
162 ira 60 
    def procE(self):
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        print 'procE(%s) ->' % (self.str[self.strpos:])
163 ira 62 
 
162 ira 63 
        return self.procT() and self.procEprm()
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163 ira 65 
    def procEprm(self):
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        # Check empty str
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        if self.strpos >= len(self.str):
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            return True
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        print 'procEprm(%s) ->' % (self.str[self.strpos:])
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        # Check +
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        if self.str[self.strpos] == '+':
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            self.strpos += 1
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            return self.procT() and self.procEprm()
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        # Check -
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        if self.str[self.strpos] == '-':
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            self.strpos += 1
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            return self.procT() and self.procEprm()
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        # We accept empty str, so take it
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        return True
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162 ira 85 
    def procT(self):
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        print 'procT(%s) ->' % (self.str[self.strpos:])
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163 ira 88 
        return self.procF() and self.procTprm()
162 ira 89 
 
163 ira 90 
    def procTprm(self):
162 ira 91 
        # Check empty str
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        if self.strpos >= len(self.str):
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            return True
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163 ira 95 
        print 'procTprm(%s) ->' % (self.str[self.strpos:])
162 ira 96 
 
163 ira 97 
        # Check *
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        if self.str[self.strpos] == '*':
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            self.strpos += 1
163 ira 100 
            return self.procF() and self.procTprm()
162 ira 101 
 
163 ira 102 
        # we accept empty str, so take it
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        return True
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    def procF(self):
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        print 'procF(%s) ->' % (self.str[self.strpos:])
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        # Check x
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        if self.str[self.strpos] == 'x':
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            self.strpos += 1
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            return self.procV()
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        # Check (E)
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        if self.str[self.strpos] == '(':
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            self.strpos += 1
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            if self.procE():
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                if self.str[self.strpos] == ')':
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                    return True
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            return False
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        # Must be a number
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        return self.procN()
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    def procN(self):
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        print 'procN(%s) ->' % (self.str[self.strpos:])
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        if self.str[self.strpos] in '0123456789':
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            self.strpos += 1
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            return True
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162 ira 133 
        return False
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163 ira 135 
    def procV(self):
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        print 'procV(%s) ->' % (self.str[self.strpos:])
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        return self.procN()
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161 ira 140 
if __name__ == '__main__':
162 ira 141 
    rdp = RecursiveDescentParser()
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    rdp.main_menu()
161 ira 143