Python - Using recursive to replace string in python

Question

I have written a recursive to filter the string , but the output isn't my expected, could you please help assist this ?

s2 = "Hello"
def remove_text(s):
    t = s.find(s2)
    t2 = len(s2)
    if t == -1:
        return s
    else:
        if t == 0:
            s = s[t2+1:]
        else:
            s = s[0:t-1] + s[t+len(s2):] 
    if s.find(s2) >= 0: #if still found s2 in s 
        remove_text(s) 

s1 = "Hello my name is XXX Hello 12345 6 "
s3 = remove_text(s1)
print(s3)

the output i got always is "None" . I expected the output is:

my name is XXX 12345 6

I think you mean to return remove_text(s) in the last line of your function. — hilberts_drinking_problem
– hilberts_drinking_problem, Commented Jan 9, 2022 at 7:51
You don't have any return statement in your first else and exactly this is the case here, you've got a Hello in your statement. Do you need to do it recursively, because otherwise the fastest way is to use the text.replace("Hello", "") — baskettaz
– baskettaz, Commented Jan 9, 2022 at 7:55

dabdya · Accepted Answer · 2022-01-09 07:55:07Z

1

s2 = "Hello"
def remove_text(s):
    t = s.find(s2)
    t2 = len(s2)
    if t == -1:
        return s
    else:
        if t == 0:
            s = s[t2+1:]
        else:
            s = s[0:t-1] + s[t+len(s2):] 
    if s.find(s2) >= 0: #if still found s2 in s 
        s = remove_text(s) 
    return s

s1 = "Hello my name is XXX Hello 12345 6 "
s3 = remove_text(s1)
print(s3)

You forgot to write return. It is not enough to add return only at the end, so it is better to assign the result of a recursive call to the string s, and then return s

answered Jan 9, 2022 at 7:55

dabdya

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Comments

nikeros · Accepted Answer · 2022-01-09 08:48:10Z

You else does not return anything You could write in a more compact way as follows:

def remove_text(input_str, to_remove):
    idx, len2 = input_str.find(to_remove), len(to_remove)
    if idx == -1:
        return input_str
    else:
        return remove_text(input_str[:max(0, idx - 1)] + input_str[idx + len2:], to_remove) 
        
result = remove_text("Hello my name is XXX Hello 12345 6 ", "Hello")

print(result)

OUTPUT

my name is XXX 12345 6

Even if I would not recommended in the specific case, you could achieve similar results without using return running something like this:

def remove_text(to_remove):
    global input_str
    idx, len2 = input_str.find(to_remove), len(to_remove)
    if idx > -1:
        input_str = input_str[:max(0, idx - 1)] + input_str[idx + len2: ]
        remove_text(to_remove)
    
input_str = "Hello my name is XXX Hello 12345 6 "
remove_text("Hello")
print(input_str)

In this case, remove_text will work recursively on the global input_str defined outside its natural scope: practically, you would need to have input_str defined outside the function before calling it.

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