This is mostly a logic problem. I am trying to replace a character in a string without using the replace function. I am trying to first change it into a list, change the elements, then turn it back into string. My attept:
def changeCar(ch,ca1,ca2):
a=list(ch)
for x in a:
if x==ca1:
x==ca2
return a
However this doesn't work. Besides, I am not sure how to transform it back into a string.
You don't need to define a string as a list in python.
string = 'The quick brown fox jusmps over the lazy dog'
# Define your variables
result = ''
for i in string:
if i == 'o':
i = '0'
result += i
print result
If you MUST however use a list:
string = list('The quick brown fox jusmps over the lazy dog')
result = []
for i in string:
if i == 'o':
i = '0'
result.append(i)
print ''.join(result)
You're on the right track. Since Python strings are immutable, you aren't able to change the characters in place, so the approach of spliting it into a list of characters, modifying the elements inside that list, and then re-joining it is correct. Your solution isn't working because x isn't a reference (or pointer) to the elements inside the list, but a copy of them. Thus, x = c2 (and not x == c2, as your example shows) only modifies the copy. You'll have to access the list by index, like so:
for ind in range(len(a)):
if a[ind] == ca1:
a[ind] = ca2
return "".join(a)
You can also use a list comprehension for maximum brevity, though it might be a little unreadable:
return "".join([(char if char != ca1 else ca2) for char in ch])
Don't change the string into a list. That's unnecessary. Instead, define an empty string in the function definition and then append to it accordingly and in the end return the value of that variable:
def changeCar(ch,ca1,ca2):
b = ''
for x in ch:
if x!= ca1:
b+= x
else:
b+=ca2
return b
Now you get:
>>> changeCar("abc","b","c")
'acc'
>>>
a == b is a Comparison Expression. a = b is an Assignment Statement. To turn a list into a string:
>>> ''.join(['a', 'b', 'c', 'd', 'e', 'f', 'g'])
'abcdefg'
>>>
For simple manipulations like this you can use list comprehensions. Try it like this:
In [1]: text = "Hello, World!"
In [2]: ''.join([ch if ch != 'o' else 'a' for ch in text])
Out[2]: 'Hella, Warld!'
This list comprehension replaces the character 'o' with 'a'
