Find common words in two strings using Python

Sample code snippet to find the common characters or words in two given strings excluding spaces. Implemented using built-in string methods in Python.

Common characters in two strings

To find common characters in two strings, we first fetch the unique characters in each by converting these to sets.
Then do a comparison within a loop to identify matching characters.

str1 = 'This is a test string'
str2 = 'This is another string'

str1 = str1.lower().replace(" ", "")
str2 = str2.lower().replace(" ", "")

charsinstr1 = list(set(str1.strip()))
charsinstr2 = list(set(str2.strip()))

commonchars = []
for c in charsinstr1:
    if (c in charsinstr2):
        commonchars.append(c)

print(commonchars)
print(len(commonchars))

Output: ['s', 'h', 'g', 'a', 'i', 'r', 'n', 'e', 't'] 9

Common words in two strings

Here, we will first convert the string to a list of words using split function.
Then loop through each word and compare.

str1 = 'This is a test string'
str2 = 'This is another string'

wordsinstr1 = str1.lower().split()
wordsinstr2 = str2.lower().split()

commonwords = []
for word in wordsinstr1:
    if (word in wordsinstr2):
        commonwords.append(word)

print(commonwords)
print(len(commonwords))

Output: ['this', 'is', 'string'] 3

Another easy way is to use list comprehension without using the for loop.
Sample below.

str1 = 'This is a test string'
str2 = 'This is another string'

commonwords = [ w for w in str1.lower().split() if (w in str2.lower().split()) ]
print(commonwords)
print(len(commonwords))

Output: ['this', 'is', 'string'] 3