how to see if a string is in a list and then update string

Question

I am trying to implement a transition function. I have stored the transitions in a list:

def transistion(self, input):
    self.currentState = 'q1'
    self.delta = "[['q1', '0', 'q2'], ['q1', '1', 'q1']]"
    k = ast.literal_eval(self.delta)
    delta_list = [[x[0],tuple(x[1:])] for x in k]
    print(delta_list)

print(delta_list) # [['q1', ('0', 'q2')], ['q1', ('1', 'q1')]]

I need to:

search delta_list to see if the self.currentState is a first element in one of the lists
if the first element was found, check that list and see if the first element of the tuple is equal to input
if the input value was also found, set self.currentState equal to the second element of the tuple

You didn't "store them in a list comprehension". You used a list comprehension to store them in a list. — Andrew Jaffe, Dec 04 '14 at 15:39
As a side note, the "question" itself (=> the 'I need to' part) is pretty trivial. What have you tried that didn't work ? — bruno desthuilliers, Dec 04 '14 at 15:43
duplicate of this one http://stackoverflow.com/questions/27289287/how-to-parse-a-string-into-a-dictionary/27289395#27289395 — Hackaholic, Dec 04 '14 at 15:48
@Hackaholic Not sure this is a dupe. Yeah, it's parsing and mentions ast.literal_eval, but the real question was about what to do next. The OP had at least gotten the string parsed to a list - one way or another. — kdopen, Dec 04 '14 at 16:06
@Hackaholic : the current question is NOT a duplicate of http://stackoverflow.com/q/27289287/41316 — bruno desthuilliers, Dec 04 '14 at 16:07

score 1 · Answer 1 · answered Dec 04 '14 at 16:05

Just to get you started, this

def transistion(self, input):
    self.currentState = 'q1'
    self.delta = "[['q1', '0', 'q2'], ['q1', '1', 'q1']]"
    k = ast.literal_eval(self.delta)
    delta_list = [[x[0],tuple(x[1:])] for x in k]
    print(delta_list)

can be more simply done as:

def transistion(self, input):
    self.currentState = 'q1'
    self.delta = eval("[['q1', '0', 'q2'], ['q1', '1', 'q1']]")
    delta_list = [[x[0],tuple(x[1:])] for x in self.delta]
    print(delta_list)

But why bother, unless this is a test harness? You can just set delta_list to exactly what you want - even in a test harness

delta_list = [['q1',('0','q2')],['q1', ('1', 'q1')]]

At this point, it's a basic for loop:

for t in delta_list:
    if self.current_state == t[0]:
        # rest of checks and actions. break if you change current state

But why bother with the tuples? You can just work with the original list of lists

how to see if a string is in a list and then update string

1 Answers1