CODEWITHSUNDEEP
python-3.xwhile-loop
user2489861
user2489861

Reputation: 109

Python: Return string using while loop (no methods or for loops)

So I have this function below where I want to return a new string where every ch is replaced with ch2:

def replace(s, ch, ch2):
'''(str, str, str) - > str
Return a new string where every instance of ch in s is replaced with ch2
Precondition: len(ch) == 1 and len(ch2) == 1
'''

i = 0
m = s[i]
while i < len(s):
    if s[i] == ch:
        return ch2
    m = m + s[i]
    i += 1
return m

When I type this:

replace('razzmatazz', 'z', 'r')

I want the output to be this:

'rarrmatarr'

I tried several ways, but I'm only getting 'r' or 'rr'.

Can someone tell me where I went wrong?

Upvotes: 0

Views: 3803

Answers (5)

Muthu Ganapathy Nathan
Muthu Ganapathy Nathan

Reputation: 3307

I think your code should be., 

i = 0
m = s[i]
while i < len(s):
    if s[i] == ch:
        m = m + ch2 // Here you are lagging.
     else   
        m = m + s[i]
    i += 1
return m

Because , In your code, when in the string razzmatazz if first z is matched then instead of replacing., it returns the ch2 i.e r. Hence you are getting r.

Upvotes: 1

Esenti
Esenti

Reputation: 707

Your're returning ch2 from the function as soon as you find ch in your original string, so that can't work in the way you expect it to do. You have to add the correct character to a new string, and then return that string after you iterate over every character in the original string.

i = 0
m = ''
while i < len(s):
    m += ch2 if s[i] == ch else s[i]
    i += 1

return m

Also, as pointed in the other answers, there are better ways to accomplish this.

Upvotes: 2

Johan Lundberg
Johan Lundberg

Reputation: 27028

This is built in to the language

'razzmatazz'.replace('z', 'r')

'rarrmatarr'

If I would use your style I would write something more along the lines of: 

def replace(s, ch, ch2):
    s2 = list(s)
    i=0
    while i < len(s):
        if s2[i] == ch:
            s2[i]=ch2
        i=i+1
    return "".join(s2)

Upvotes: 0

Blender
Blender

Reputation: 298176

return immediately returns a value and exits the function, even if it's in a loop. You probably want to get rid of that while loop and use a nice for loop instead:

def replace(s, ch, ch2):
    '''(str, str, str) - > str
    Return a new string where every instance of ch in s is replaced with ch2
    Precondition: len(ch) == 1 and len(ch2) == 1
    '''

    result = ''

    for char in s:
        if char == ch:
            result += ch2
        else:
            result += char

    return result

Although it'd be better if you just used the built-in str.replace method:

def replace(s, ch, ch2):
    return s.replace(ch, ch2)

Or more concisely:

replace = str.replace

Upvotes: 0

carl-lopez
carl-lopez

Reputation: 582

Why don't you use str.replace(), available in Python?

>>> s = 'razzmatazz'
>>> s.replace('z', 'r')
'rarrmatarr'

No need to create a custom function to get done what you want

Upvotes: 0

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