python - How are finite automata implemented in code? -


how 1 implement dfa or nfa matter in python code?

what ways in python? , ever used in real world projects?

a straightforward way represent dfa dictionary of dictionaries. each state create dictionary keyed letters of alphabet , global dictionary keyed states. example, following dfa wikipedia article on dfas

enter image description here

can represented dictionary this:

dfa = {0:{'0':0, '1':1},        1:{'0':2, '1':0},        2:{'0':1, '1':2}}

to "run" dfa against input string drawn alphabet in question (after specifying initial state , set of accepting values) straightforward:

def accepts(transitions,initial,accepting,s):     state = initial     c in s:         state = transitions[state][c]     return state in accepting

you start in initial state, step through string character character, , @ each step next state. when done stepping through string check if final state in set of accepting states.

for example

>>> accepts(dfa,0,{0},'1011101') true >>> accepts(dfa,0,{0},'10111011') false

for nfas store sets of possible states rather individual states in transition dictionaries , use random module pick next state set of possible states.


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