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What code goes in #TODOs?

What code goes in #TODOs?

Database System Concepts
Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
Problem 1PE
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What code goes in #TODOs?

# TODO: This is your class for modeling NFAS/DFAS! Some is already stubbed out for you. class NFA: """A class for NFAS that can be constructed from a Regex""" def _init_(self, r = None): """Constructs an empty-language NFA when r==None, or constructs an NFA from the provided Regex object.""" self.r = r #s Save a reference to the regex itself if r == None: # If no Regex instance is provided: the empty language start = State() self.Q = {start} self.Sigma = set() self.s = start self.F = set() self.delta = set() elif isinstance(r, EpsilonRegex): pass # TODO: the epsilon language, base form (Hint: look in regex.py) elif isinstance(r, StarRegex): pass # TODO: handle derived form star elif isinstance(r, SeqRegex): pass # TODO: handle derived form juxtaposition/sequencing elif isinstance(r, DisjRegex): # Note how this is exactly the Disjunction construction # we saw in the slides for converting RE -> NFA nfað = NFA(r.r@) nfa1 = NFA(r.r1) start = State() end = State() # TODO: what about self.Q? self.Sigma = nfa®.Sigma | nfa1.Sigma # TODO: what about self.s? self.F = {end} # Explanation: below, min nice for selecting an arbitrary # element; as we maintain as an invariant that self.F is # a singleton for the duration of NFA construction, this works well # (may not be the case for DFAS; also note: empty string is epsilon) self.delta = ({(start, ', nfa®.s), (start, "", nfa1.s), (min(nfa®.F), "", end), (min(nfa1.F), "", end)} | nfað.delta | nfa1.delta) elif isinstance(r, CharRegex): pass # TODO: handle base form (Hint: look in regex.py) else: raise "NFA must be constructed from a Regex (or None)."
Transcribed Image Text:# TODO: This is your class for modeling NFAS/DFAS! Some is already stubbed out for you. class NFA: """A class for NFAS that can be constructed from a Regex""" def _init_(self, r = None): """Constructs an empty-language NFA when r==None, or constructs an NFA from the provided Regex object.""" self.r = r #s Save a reference to the regex itself if r == None: # If no Regex instance is provided: the empty language start = State() self.Q = {start} self.Sigma = set() self.s = start self.F = set() self.delta = set() elif isinstance(r, EpsilonRegex): pass # TODO: the epsilon language, base form (Hint: look in regex.py) elif isinstance(r, StarRegex): pass # TODO: handle derived form star elif isinstance(r, SeqRegex): pass # TODO: handle derived form juxtaposition/sequencing elif isinstance(r, DisjRegex): # Note how this is exactly the Disjunction construction # we saw in the slides for converting RE -> NFA nfað = NFA(r.r@) nfa1 = NFA(r.r1) start = State() end = State() # TODO: what about self.Q? self.Sigma = nfa®.Sigma | nfa1.Sigma # TODO: what about self.s? self.F = {end} # Explanation: below, min nice for selecting an arbitrary # element; as we maintain as an invariant that self.F is # a singleton for the duration of NFA construction, this works well # (may not be the case for DFAS; also note: empty string is epsilon) self.delta = ({(start, ', nfa®.s), (start, "", nfa1.s), (min(nfa®.F), "", end), (min(nfa1.F), "", end)} | nfað.delta | nfa1.delta) elif isinstance(r, CharRegex): pass # TODO: handle base form (Hint: look in regex.py) else: raise "NFA must be constructed from a Regex (or None)."
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