仅接受一种形式的定界符并拒绝多种类型的简单方法？

Question

I was wondering how I could go about making something that accepts a string with only one type of delimiter, something like this:

car:bus:boat

and rejecting something like:

car:bus-boat

I am not really sure about how to go about creating something like this.

Answer 1

Well, first you have to define what are invalid limiters. A hyphen could well be part of a valid hyphenated word or name, and the algorithm wouldn't be able to tell those apart. Supposing you have a list of invalid delimiters, you could just do:

def string_is_valid(s):
    invalid_delimiters = ['-', ';']
    for d in invalid_delimiters:
        if d in s:
            return False
    return True

s1 = 'car:bus-boat'

print(string_is_valid(s1))  # False

s2 = 'car:bus:boat'

print(string_is_valid(s2))  # True

If, on the other hand, you have a list of delimiters and you want to make sure that only one type is present on the string, you could do this:

def string_is_valid(s):
    valid_delimiters = [',', ':', ';']

    # For each delimiter in our list...
    for d in valid_delimiters:
        # If the delimiter is present in the string...
        if d in s:
            # If any of the other delimiters is in s (and the other delimiter isn't the same one we're currently looking at), return False (it's invalid)
            if any([other_d in s and other_d != d for other_d in valid_delimiters]):
                return False
    return True


s1 = 'car:bus:boat'
print(string_is_valid(s1))  # True

s2 = 'car,bus,boat'
print(string_is_valid(s2))  # True

s3 = 'car,bus;boat'
print(string_is_valid(s3))  # False

Answer 2

you can have an alphabet of "allowed" characters and count whatever is not on it (hence interpreting it as a sep).

eg

allowed = list('abcdefghijklmnopqrstuvxwyz')
def validate(string):
    if len(set([k for k in string if k not in allowed])) > 1:
         return False
    return True

Of course you can expand the allowed for capital letters etc.

Answer 3

Use regex expression:

import re
data = re.compile(r'^([a-zA-Z][:][a-zA-Z]){1, }$') 
data.match(string)