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 a list of stings, and I want to filter out all of them except the words that are ONLY made up of ANY of the letters in another string. For example, filtering ['aba', 'acba', 'caz'] though 'abc' should give ['aba', 'acba']. (z not in abc)

Just like only keeping the items that can be made using the given letters.

Answer 1

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 2

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 3

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']