检查后将字符串追加到列表

Question

I was writing a small game which requires just a thing in which when user enters a string it should check if the word is made from the alphabets given and then it should append to a new list.

user_input = raw_input("Please enter a word: ")
ls = ["a", "f" , "x" , "u"]
user_list = []

for i in user_input:
    if i in ls:
        user_list.append(user_input)

But the problem is that if any of the string is matched the whole word gets appended to the list. Like fun , aim would get appended to the list.

Answer 1

I would use a set . Your allowed alphabet could be a set, and then make a set out of your user's word. If the user specified set is a subset of the alphabet set, then you'll know that the word is composed exclusively of characters from the desired alphabet.

user_input = raw_input("Please enter a word: ")
ls = set('afxu')
user_list = []

if set(user_input).issubset(ls):
    user_list.append(user_input)

Answer 2

You should use a boolean and only add if all letters from the input are in your dictionary:

user_input = raw_input("Please enter a word: ")
ls = ["a", "f" , "x" , "u"]
user_list = []
inDict = True

for i in user_input:
    if not(i in ls):
        inDict = False
        break
if(inDict):    
    user_list.append(user_input)

Answer 3

Another answer for condition using sets is

user_input = raw_input("Please enter a word: ")
ls = ["a", "f" , "x" , "u"]
user_list = []


if set(list(user_input)).issubset(set(ls)):
    user_list.append(user_input)

Answer 4

You need to check if each letter in user_input is in you list of allowable letters (which you should probably rename to letter_list or something else as ls is a reserved word in IPython).

One way to do this is to use reduce with a lambda function:

if reduce(lambda a, b: a and b, [letter in ls for letter in user_input]):
    user_list.append(user_input)

Answer 5

You can check if all the characters in user_input are in ls

if all(char in ls for char in user_input) 

i in ls will evaluate to True or False, if we hit a char not in ls the loop will short circuit and return False, if all the chars in user_input are in ls it will return True and the word will be appended.

It does not make much sense to create a list for single word and append but if you really want it you can use a list comp:

user_list  = [user_input for i in user_input  if all(char in ls for char in user_input)]

If you are actually wanting to take multiple words, then you can split and check each word:

user_list  = [word for word in user_input.split() if all(char in ls for char in word)]

Using your own code you would have to check every character first and only append after every char has been checked but using all is a much better approach.

For large input making ls a set ls = {"a", "f" , "x" , "u"} would be a more efficient approach as set lookups are 0(1) but for small input sizes it would not make any real difference