Passing off strings to “alphabet” that contains specific characters for lexical analysis

In python, I want to know how I can pass off the strings that checks:

I am having a hard time figuring out the syntax and I specifically need strings like these instead of using built-in functions for lexical analysis. The following will clear the idea of what I'am trying to do:

alphanumeric=r'[a-zA-Z]+'
digit=r'[0-9]'
other=r'![a-zA-Z_0-9]'
alphabet = alphanumeric ,digit,other


This alphabet along with other DFA attributes will be fed into the dfa object's function run_with_input_list() with some user defined string. The dfa class structure is below:

class DFA:
current_state = None

def __init__(self, states, alphabet, transition_function, start_state, accept_states): #5-tupple
self.states = states
self.alphabet = alphabet
self.transition_function = transition_function
self.start_state = start_state
self.accept_states = accept_states
self.current_state = start_state
return

def transition_to_state_with_input(self, input_value):
if ((self.current_state, input_value) not in self.transition_function.keys()):
self.current_state = None
return
self.current_state = self.transition_function[(self.current_state, input_value)]
return

def in_accept_state(self):
if self.current_state in self.accept_states:
print("String Accepted")
else:
print("String Rejected")

def go_to_initial_state(self):
self.current_state = self.start_state
return

def run_with_input_list(self, input_list):
self.go_to_initial_state()
for inp in input_list:
self.transition_to_state_with_input(inp)
continue
return self.in_accept_state()

pass

def validity(self,input_list): #checking whether the input string is valid
for a in input_list:
if a in self.alphabet:
continue
else:
print("Invalid String")
return 0
return 1


3 Answers
3

I did not quite understand what "passing off" means, but these are the methods you can use :

1) Check if it contains only alphabets

print("abcd".isalpha()) #True
print("abcd123".isalpha()) #False
print("123".isalpha()) #False


2) Check if it contains only numbers

print("123".isnumeric()) #True
print("abcd".isnumeric()) #False
print("abcd123".isnumeric()) #False


3) Check if it contains only alphabets / numbers

print("abc123".isalnum()) #True
print("abc???".isalnum()) #False


isalpha

Python regular expressions already have special characters for this - digit has d alphanumeric has w, non-alphanumeric character has W.

d

w

W

References: https://docs.python.org/3/howto/regex.html

Python provides standard helpers for such operation, look at this example:

def what_is(s):
is_num = s.isnumeric()
is_alpha = s.isalpha()
is_other = not is_num and not is_alpha
return is_num, is_alpha, is_other


def main():
alpha = "Ciao"
num = "0102"
other = "£*+]"
print(what_is(alpha))
print(what_is(num))
print(what_is(other))


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