Re: find and remove \ character from string

[Stefan Behnel]

Konstantinos Pachopoulos wrote:
 i have the following string s and the following code, which doesn't
 successfully remove the \, but sucessfully removes the \\.
 
 s=Sad\\asd\asd
 newS=
 for i in s:
 ... if i!=\\:
 ... newS=newS+i

I'm not quite sure what you're trying to achieve, but I'd use

 r\\a\\b\c.replace(, )
'ab\\c'

 r\\a\\b\c.replace(\\, )
'abc'

Note that \\ in the source is unescaped to \ in the string. Use r\\ to
prevent that.

Stefan
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Re: find and remove \ character from string

[Steve Holden]

Konstantinos Pachopoulos wrote:
 Hi,
 i have the following string s and the following code, which doesn't 
 successfully remove the \, but sucessfully removes the \\.
 
   s=Sad\\asd\asd
   newS=
   for i in s:
 ... if i!=\\:
 ... newS=newS+i
 ...
   newS
 'Sadasd\x07sd'
 
In actual fact there was just a single backslash in s to start with. If 
you read the documentation carefully at

   http://docs.python.org/ref/strings.html

(though it's the language reference manual, and therefore not 
necessarily suitable reading for beginners)  you will see that the \\ 
represents a single backslash character and \a represents an ASCII BEL 
character (whose decimal value is 7, and which the interpreter 
represents as the hexadecimal escape string \x07).

So the characters in s were S a d \ a s d \x07 s d and you shoudl have 
seen len(s) == 10.

As has already been mentioned, the shortest way to do what you want would be

newS = s.replace(\\, )

 I have also read the following, but i do not understand the ...and the 
 remaining characters have been mapped through the given translation 
 table, which must be a string of length 256. Can some explain?
 
 *translate*(  table[, deletechars])
 
 Return a copy of the string where all characters occurring in the
 optional argument deletechars are removed, and the remaining
 characters have been mapped through the given translation table,
 which must be a string of length 256.
 
 For Unicode objects, the translate() method does not accept the
 optional deletechars argument. Instead, it returns a copy of the s
 where all characters have been mapped through the given translation
 table which must be a mapping of Unicode ordinals to Unicode
 ordinals, Unicode strings or |None|. Unmapped characters are left
 untouched. Characters mapped to |None| are deleted. Note, a more
 flexible approach is to create a custom character mapping codec
 using the codecs http://docs.python.org/lib/module-codecs.html
 module (see encodings.cp1251 for an example).
 
The translate() string method uses the numeric represetation of each 
character as an index into the translation table. So a null translation 
table can be constructed using

  t = .join(chr(i) for i in range(256))
  t
'\x00\x01\x02\x03\x04\x05\x06\x07\x08\t\n\x0b\x0c\r\x0e\x0f\x10\x11\x12\x13\x14\
x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f 
!#$%\'()*+,-./0123456789:;=[EMAIL PROTECTED]
DEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~\x7f\x80\x81\x82\x83
\x84\x85\x86\x87\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f\x90\x91\x92\x93\x94\x95\x96\x97
\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f\xa0\xa1\xa2\xa3\xa4\xa5\xa6\xa7\xa8\xa9\xaa\xab
\xac\xad\xae\xaf\xb0\xb1\xb2\xb3\xb4\xb5\xb6\xb7\xb8\xb9\xba\xbb\xbc\xbd\xbe\xbf
\xc0\xc1\xc2\xc3\xc4\xc5\xc6\xc7\xc8\xc9\xca\xcb\xcc\xcd\xce\xcf\xd0\xd1\xd2\xd3
\xd4\xd5\xd6\xd7\xd8\xd9\xda\xdb\xdc\xdd\xde\xdf\xe0\xe1\xe2\xe3\xe4\xe5\xe6\xe7
\xe8\xe9\xea\xeb\xec\xed\xee\xef\xf0\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9\xfa\xfb
\xfc\xfd\xfe\xff'
 

(the above output will look a little screwy in the mail because of odd 
line wrapping).

So hopefully you could then achieve the same effect (at vastly greater 
complexity than the first solution) using

  s=Sad\\asd\asd
  len(s)
10
  newS = s.translate(t, \\)
  newS
'Sadasd\x07sd'
 

You would probably only want to use that method if you were actually 
translating some of the characters at the same time.

regards
  Steve
-- 
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Holden Web LLC/Ltd   http://www.holdenweb.com
Skype: holdenweb  http://del.icio.us/steve.holden

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Re: find and remove \ character from string

[I V]

On Sat, 15 Sep 2007 19:34:45 +0300, Konstantinos Pachopoulos wrote:
 Hi,
 i have the following string s and the following code, which doesn't
 successfully remove the \, but sucessfully removes the \\.

There is no \\ in the string; there's one \ , which gets succesfully 
removed.

   s=Sad\\asd\asd

When you write a string in the source code \\ gets changed to \ and \a 
gets changed to ASCII Bell (BEL) (that's what the docs say), which is a 
(non-printable) control code that is supposed to make the terminal beep.

   newS=
   for i in s:
 ... if i!=\\:

Here, your test is true if i is not \

 ... newS=newS+i
 ...
   newS
 'Sadasd\x07sd'

And here, you have a string containing no backslashes, but containing a 
character with ASCII code 7; it turns out that ASCII code 7 is the ASCII 
Bell, i.e., the character that you added to the string when you wrote 
'\a'.
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