Test if string ONLY contains given characters

Question

What\'s the easiest way to check if a string only contains certain specified characters in Python? (Without using RegEx or anything, of course)

Specifically, I have

Answer 1

Something like this:

strings = ['aba', 'acba', 'caz']
given = "abc"
filter(lambda string: all(char in given for char in string), strings)

Answer 2

Assuming the discrepancy in your example is a typo, then this should work:

my_list = ['aba', 'acba', 'caz']
result = [s for s in my_list if not s.strip('abc')]

results in ['aba', 'acba']. string.strip(characters) will return an empty string if the string to be stripped contains nothing but characters in the input. Order of the characters should not matter.

Answer 3

You can make use of sets:

>>> l = ['aba', 'acba', 'caz']
>>> s = set('abc')
>>> [item for item in l if not set(item).difference(s)]
['aba', 'acba']

Answer 4

Assuming you only want the strings in your list which have only the characters in your search string, you can easily perform

>>> hay = ['aba', 'acba', 'caz']
>>> needle = set('abc')
>>> [h for h in hay if not set(h) - needle]
['aba', 'acba']

If you wan't to avoid sets, you can also do the same using str.translate. In this case, you are removing all characters which are in your search string.

>>> needle = 'abc'
>>> [h for h in hay if not h.translate(None,needle)]
['aba', 'acba']

Answer 5

I will assume your reluctance for regexp is not really an issue :

strings = ['aba', 'acba', 'caz']
given = "abc"
filter(lambda value: re.match("^[" + given + "]$", value), strings)

Answer 6

Below is the code:

a = ['aba', 'acba', 'caz']
needle = 'abc'

def onlyNeedle(word):
    for letter in word:
        if letter not in needle:
            return False

    return True

a = filter(onlyNeedle, a)

print a