Python: loop and edit string character

I’m new to python and coding in general. Here is a problem from my homework, as well as my current code. I know that I only have one of the parts, but I wanted to figure this one out before moving on to the rest. With my loop, I can find and identify the letter i, but I can’t figure out how to change the i’s to 1’s.

Problem:

Many user-created passwords are simple and easy to guess. Write a
program that takes a simple password and makes it stronger by
replacing characters using the key below, and by appending "!" to the
end of the input string.

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i becomes 1
a becomes @
m becomes M
B becomes 8
s becomes $

Ex: If the input is:

mypassword

the output is:

Myp@$$word!

Hint: Python strings are immutable, but support string concatenation.
Store and build the stronger password in the given password variable.

Code:

word = input()
password = ()


for letter in word:
    if letter == 'i':
        password = password+'1'
    else: password = password+letter

print(password)

input: igigigig
output: igigigig

>Solution :

First off, you’re initializing your password to an incorrect variable choice. password = () sets password to a tuple. Attempting to add characters to a tuple variable will lead to an exception:

>>> password = ()
>>> password = password + '1'
Traceback (most recent call last):
  File "<input>", line 1, in <module>
TypeError: can only concatenate tuple (not "str") to tuple

Next, you have a mapping of characters provided in the question. You can start by creating a dictionary to represent this mapping.

mapping = {
    'i': '1',
    'a': '@',
    'm': 'M',
    'B': '8',
    's': '$',
}

When looping against letters you can use the mapping to determine if a replacement should be made:

for letter in word:
    if letter in mapping:
        password = password + mapping.get(letter)
    else:
        password = password + letter

You also forgot to add the ! to the end.

Final result:

mapping = {
    'i': '1',
    'a': '@',
    'm': 'M',
    'B': '8',
    's': '$',
}

word = "mypassword"
password = ""

for letter in word:
    if letter in mapping:
        password = password + mapping[letter]
    else:
        password = password + letter
password += "!"

print(password)

Simplifying this further:

for letter in word:
    password += mapping.get(letter, letter)
password += "!"

Even further with a comprehension!:

password = ''.join(mapping.get(l, l) for l in word) + "!"