Find common characters between two strings

I am trying to print the common letters from two different user inputs using a for loop. (I need to do it using a for loop.) I am running into two problems: 1. My statement “If char not in output…” is not pulling unique values. 2. The output is giving me a list of individual letters rather than a single string. I tried the split the output but split ran into a type error.

wrd = 'one'
sec_wrd = 'toe'

def unique_letters(x): 
    output =[]
    for char in x: 
        if char not in output and char != " ": 
            output.append(char)
    return output

final_output = (unique_letters(wrd) + unique_letters(sec_wrd))

print(sorted(final_output))

Answer

You are trying to perform the Set Intersection. Python has set.intersection method for the same. You can use it for your use-case as:

>>> word_1 = 'one'
>>> word_2 = 'toe'

#    v join the intersection of `set`s to get back the string
#    v                             v  No need to type-cast it to `set`.
#    v                             v  Python takes care of it
>>> ''.join(set(word_1).intersection(word_2))
'oe'

set will return the unique characters in your string. set.intersection method will return the characters which are common in both the sets.

---

If for loop is must for you, then you may use a list comprehension as:

>>> unique_1 = [w for w in set(word_1) if w in word_2]
# OR
# >>> unique_2 = [w for w in set(word_2) if w in word_1]

>>> ''.join(unique_1)  # Or, ''.join(unique_2)
'oe'

Above result could also be achieved with explicit for loop as:

my_str = ''
for w in set(word_1):
    if w in word_2:
        my_str += w

# where `my_str` will hold `'oe'`