[Tutor] How to change the char in string for Python

[Sudo Nohup]

Thanks very much!!

I learnt a lot from you kind reply. Not only is it about the question
itself, but also about how to ask a question in a mailing list.(Sorry that
it is the first time for me to ask questions in a mailing list).

The question comes from a riddle of the PythonChallenge website(
http://www.pythonchallenge.com/pc/def/map.html).

Now I write the code as the following,

mystring = "g fmnc wms bgblr rpylqjyrc gr zw fylb. rfyrq ufyr amknsrcpq ypc
dmp. bmgle gr gl zw fylb gq glcddgagclr ylb rfyr'q ufw rfgq rcvr gq qm
jmle. sqgle qrpgle.kyicrpylq() gq pcamkkclbcb. lmu ynnjw ml rfc spj."
temp = [ chr ( (ord(char)-ord('a')+2)%26 +ord('a'))  if
(ord(char)>=ord('a') and ord(char)<=ord('z')) else char  for char in
mystring ]
result = "".join(temp)
print result

OR

mystring = "g fmnc wms bgblr rpylqjyrc gr zw fylb. rfyrq ufyr amknsrcpq ypc
dmp. bmgle gr gl zw fylb gq glcddgagclr ylb rfyr'q ufw rfgq rcvr gq qm
jmle. sqgle qrpgle.kyicrpylq() gq pcamkkclbcb. lmu ynnjw ml rfc spj."
result = []
for char in mystring:
    if(ord(char)>=ord('a') and ord(char)<=ord('z')):
        char = chr ( (ord(char)-ord('a')+2)%26 +ord('a'))
    result.append(char)
result = "".join(result)
print result

Thanks,
James


On Sun, Feb 24, 2013 at 8:40 PM, Dave Angel <davea at davea.name> wrote:

> Both your later remarks are top-posted, ruining the sequence of who posted
> what.
>
>
> On 02/24/2013 06:57 AM, Sudo Nohup wrote:
>
>> Thanks for your help.
>>
>> I just found a webpage used for me:
>> http://stackoverflow.com/**questions/10017147/python-**
>> replace-characters-in-string<http://stackoverflow.com/questions/10017147/python-replace-characters-in-string>
>>
>> That page provides some other solutions. Thanks!
>>
>> On Sun, Feb 24, 2013 at 7:47 PM, Asokan Pichai <pasokan at talentsprint.com>
>> **wrote:
>>
>>  On Feb 24, 2013 4:27 PM, "Sudo Nohup" <sudo.nohup at gmail.com> wrote:
>>>
>>>>
>>>> Dear all,
>>>>
>>>> I want to change the value of a char in a string for Python. However, It
>>>>
>>> seems that "=" does not work.
>>>
>>
> assignment works fine, when it's really assignment.  But it doesn't work
> inside an expression, and you cannot change an immutable object in place.
>
>
>
>>>> Could you help me? Thanks!
>>>>
>>>> str = "abcd"
>>>> result = [char = 'a' for char in str if char == 'c']
>>>>
>>>
> In a list comprehension, the if expression is used to skip items from the
> sequence.  So the above form, modified, might be used to remove selected
> characters from the string.
>
> By the way, since 'str' is a builtin, it's a bad practice to take it over
> for your own use.  For example, what if you subsequently needed to convert
> an int to a string?
>
>
>
>>>>
>>>> OR:
>>>>
>>>> str = 'abcd'
>>>> for char in str:
>>>>      if char == 'a':
>>>>         char = 'c'
>>>>
>>>
> You create a new object, and bind it to char, but then you don't do
> anything with it.
>
>
>
>>>>
>>>> OR:
>>>>
>>>> str = 'abcd'
>>>> for i in range(len(str)):
>>>>      if str[i] == 'a':
>>>>         str[i] = 'c'
>>>>
>>>> (
>>>> Traceback (most recent call last):
>>>>    File "<stdin>", line 3, in <module>
>>>> TypeError: 'str' object does not support item assignment
>>>> )
>>>>
>>>
> A string object is immutable, so that you cannot use assignment to replace
> portions of it.
>
>
>
>>> Look up string replace function.
>>>
>>>
>>
> That of course is the simplest answer to the problem as originally given.
>
> (Here is where your amendment to the problem should have been given,
> rather than top-posting it.)
>
> But you now say you're planning to replace all the characters in the
> string, according to a formula.
>
> What yo should have specified in the first place is what version of Python
> you're using.  I'll assume 2.7
>
> This amended problem would lend itself nicely to translate(), and the link
> you posted does mention that.
>
> But there are several other approaches, similar to the ones you already
> tried, and sometimes one of them is more interesting or useful.
>
> For example, a list comprehension very close to what you tried would work
> fine (untested):
>
> temp = [ chr( ord(char) + 2 ) for char in mystring]
> result = "".join(temp)
>
> Likewise a loop:
>
> result = []
> for char in mystring:
>     char = chr ( ord(char) + 2
>     result.append(char)
> result = "".join(result)
>
>
> --
> DaveA
>
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