Python Class – Can't find out how to use method return value within another method

So this is the class i’m testing:

class Test:

    def find_string(self, string):
        self.string = string
        return string.find(string)

    def add_string(self, string):
        found = self.find_string('bar')

        if found == -1:
            string = string + ' bar'
            
        return string

Here is my setup:

test_string = 'foo'

Test1 = Test()
new_string = Test1.add_string(string)

Results

Expected result: foo bar
Result: foo

If I replace the method call in add_string with the direct function find() it works fine. Please help me.

>Solution :

As for me all problem is that variables have similar names and this can be misleading.

Your string.find(string) means "bar".find("bar") but you expect "foo".find("bar")

You would have to use self.string = string in add_string() (instead of find_string()) and later in find_string() use self.string.find(string) instead of string.find(string) – and then you will have "foo" in self.string and "bar" in string so finally self.string.find(string) will mean "foo".find("bar")

class Test:

    def find_string(self, string):
        return self.string.find(string)

    def add_string(self, string):
        self.string = string

        found = self.find_string('bar')

        if found == -1:
            string = string + ' bar'
            
        return string

# --- main ---

test_string = 'foo'

test = Test()   # PEP8: `lower_case_names` for variables 
new_string = test.add_string(test_string)

print(new_string)

PEP 8 — Style Guide for Python Code