This question already has answers here:
Why do backslashes appear twice?
(2 answers)
Closed 8 years ago.
I need to escape a & (ampersand) character in a string. The problem is whenever I string = string.replace ('&', '\&') the result is '\\&'. An extra backslash is added to escape the original backslash. How do I remove this extra backslash?
The result '\\&' is only displayed - actually the string is \&:
>>> str = '&'
>>> new_str = str.replace('&', '\&')
>>> new_str
'\\&'
>>> print new_str
\&
Try it in a shell.
The extra backslash is not actually added; it's just added by the repr() function to indicate that it's a literal backslash. The Python interpreter uses the repr() function (which calls __repr__() on the object) when the result of an expression needs to be printed:
>>> '\\'
'\\'
>>> print '\\'
\
>>> print '\\'.__repr__()
'\\'
Python treats \ in literal string in a special way.
This is so you can type '\n' to mean newline or '\t' to mean tab
Since '\&' doesn't mean anything special to Python, instead of causing an error, the Python lexical analyser implicitly adds the extra \ for you.
Really it is better to use \\& or r'\&' instead of '\&'
The r here means raw string and means that \ isn't treated specially unless it is right before the quote character at the start of the string.
In the interactive console, Python uses repr to display the result, so that is why you see the double '\'. If you print your string or use len(string) you will see that it is really only the 2 characters
Some examples
>>> 'Here\'s a backslash: \\'
"Here's a backslash: \\"
>>> print 'Here\'s a backslash: \\'
Here's a backslash: \
>>> 'Here\'s a backslash: \\. Here\'s a double quote: ".'
'Here\'s a backslash: \\. Here\'s a double quote: ".'
>>> print 'Here\'s a backslash: \\. Here\'s a double quote: ".'
Here's a backslash: \. Here's a double quote ".
To Clarify the point Peter makes in his comment see this link
Unlike Standard C, all unrecognized
escape sequences are left in the
string unchanged, i.e., the backslash
is left in the string. (This behavior
is useful when debugging: if an escape
sequence is mistyped, the resulting
output is more easily recognized as
broken.) It is also important to note
that the escape sequences marked as
“(Unicode only)” in the table above
fall into the category of unrecognized
escapes for non-Unicode string
literals.
>>> '\\&' == '\&'
True
>>> len('\\&')
2
>>> print('\\&')
\&
Or in other words: '\\&' only contains one backslash. It's just escaped in the python shell's output for clarity.
printing a list can also cause this problem (im new in python, so it confused me a bit too):
>>>myList = ['\\']
>>>print myList
['\\']
>>>print ''.join(myList)
\
similarly:
>>>myList = ['\&']
>>>print myList
['\\&']
>>>print ''.join(myList)
\&
There is no extra backslash, it's just formatted that way in the interactive environment. Try:
print string
Then you can see that there really is no extra backslash.
Related
When I write print('\') or print("\") or print("'\'"), Python doesn't print the backslash \ symbol. Instead it errors for the first two and prints '' for the third. What should I do to print a backslash?
This question is about producing a string that has a single backslash in it. This is particularly tricky because it cannot be done with raw strings. For the related question about why such a string is represented with two backslashes, see Why do backslashes appear twice?. For including literal backslashes in other strings, see using backslash in python (not to escape).
You need to escape your backslash by preceding it with, yes, another backslash:
print("\\")
And for versions prior to Python 3:
print "\\"
The \ character is called an escape character, which interprets the character following it differently. For example, n by itself is simply a letter, but when you precede it with a backslash, it becomes \n, which is the newline character.
As you can probably guess, \ also needs to be escaped so it doesn't function like an escape character. You have to... escape the escape, essentially.
See the Python 3 documentation for string literals.
A hacky way of printing a backslash that doesn't involve escaping is to pass its character code to chr:
>>> print(chr(92))
\
print(fr"\{''}")
or how about this
print(r"\ "[0])
For completeness: A backslash can also be escaped as a hex sequence: "\x5c"; or a short Unicode sequence: "\u005c"; or a long Unicode sequence: "\U0000005c". All of these will produce a string with a single backslash, which Python will happily report back to you in its canonical representation - '\\'.
For static strings, putting an r in front of the string would give the raw string (e.g. r'some \' string'). Since it is not possible to put r in front of a unicode string variable, what is the minimal approach to dynamically convert a string variable to its raw form? Should I manually substitute all backslashes with double backslashes?
str_var = u"some text with escapes e.g. \( \' \)"
raw_str_var = ???
If you really need to escape a string, let's say you want to print a newline as \n, you can use the encode method with the Python specific string_escape encoding:
>>> s = "hello\nworld"
>>> e = s.encode("string_escape")
>>> e
"hello\\nworld"
>>> print s
hello
world
>>> print e
hello\nworld
You didn't mention anything about unicode, or which Python version you are using, but if you are dealing with unicode strings you should use unicode_escape instead.
>>> u = u"föö\nbär"
>>> print u
föö
bär
>>> print u.encode('unicode_escape')
f\xf6\xf6\nb\xe4r
Your post originally had the regex tag, maybe re.escape is what you're actually looking for?
>>> re.escape(u"foo\nbar\'baz")
u"foo\\\nbar\\'baz"
Not the "double escapes", ie printing the above string yields:
foo\
bar\'baz
There is nothing to convert - the r prefix is only significant in source code notation, not for program logic.
As a rule, if you use a single backslash in a normal string, it will automatically be converted to a double backslash if it doesn't start a valid escape sequence:
>>> "\n \("
'\n \\('
Since it may be difficult to remember all the valid/invalid escape sequences, raw string notation was introduced. But there is no way and no need to convert a string after it has been defined.
In your case, the correct approach would be to use
str_var = ur"some text with escapes e.g. \( \' \)"
which happens to result in the same string here, but is more explicit.
This question already has answers here:
python: replace a double \\ in a path with a single \
(3 answers)
Closed 8 years ago.
I Have a string having path of folder like below
>>> path
'\\\\sdgte\\ssdfdaa\\asfdsf'
I want to replace \\ with \ . I tried to replace but does not work as below
>>> path.replace('\\','\')
File "<input>", line 1
path.replace('\\','\')
^
SyntaxError: EOL while scanning string literal
Any Help will be highly appreciated.
There is no "\\" in the string. If you print it instead of looking at its representation you'll see the value that the string actually contains.
>>> print path
\\sdgte\ssdfdaa\asfdsf
You should use the escape charachter '\' to escape each \ in your string
path.replace('\\\\','\\')
you probably don't need to replace anything. \ is a special character in python that means "the next character, literally" in string literals. That is, if you want a string, containg a backslash, you'd probably type "\\":
>>> len('\\')
1
>>> print '\\'
\
>>> print '\\\\foo\\bar'
\\foo\bar
>>>
The reason you're getting that SyntaxError is the same reason you're seeing the doubled backslashes to begin with: backslash is the "escape" character, used to indicate the start of a special sequence, like "\n" for line feed, which would otherwise be difficult to represent in a string. The backslash character itself therefore has to be represented by a double backslash.
On the other hand, if you don't need to use any escape sequences within a string, you can preface the string with "r" instead of doubling the backslashes:
path.replace(r'\\', r'\')
path.replace(r'\\', '\\')
"r" indicates a "raw" string.
The problem you are running into, is that \ is an escape character. Instead of reading that as
replace '\\' with '\'
python is reading your argument as "replace the single backslash character with the single quotation mark character". The reason you are getting the error you are, is because python is ignoring your second single quotation mark because it thinks that is what you want it to do.
What you want is:
path.replace('\\\\', '\\')
you have to escape all backslashes because they are special.
I have a string This is a Test and a passed parameter s.
How can I escape all s-characters of that first string?
It should result in Thi\s i\s a Te\sT
I tried it like this:
rstr = rstr.replace(esc, r"\\" + esc)
But it will result in \\ before each s
r'\\' produces a literal double backslash:
>>> r'\\'
'\\\\'
Don't use a raw string here, just use '\\':
>>> 'This is a Test'.replace('s', '\\s')
'Thi\\s i\\s a Te\\st'
Don't confuse the Python representation with the value. To make debugging and round-tripping easy, the Python interpreter uses the repr() function to echo back results.
The repr() of a string uses Python literal notation, including escaping any backslashes:
>>> r'\s'
'\\s'
>>> len(r'\s')
2
>>> print r'\s'
\s
The actual value contains just one backslash, but because a backslash can start characters with special meanings, such as \n (a newline), or \x00 (a null byte), they are represented escaped so that you can paste the value directly back into the interpreter.
This question already has answers here:
How can I put an actual backslash in a string literal (not use it for an escape sequence)?
(4 answers)
Closed 7 months ago.
In python, I am trying to replace a single backslash ("\") with a double backslash("\"). I have the following code:
directory = string.replace("C:\Users\Josh\Desktop\20130216", "\", "\\")
However, this gives an error message saying it doesn't like the double backslash. Can anyone help?
No need to use str.replace or string.replace here, just convert that string to a raw string:
>>> strs = r"C:\Users\Josh\Desktop\20130216"
^
|
notice the 'r'
Below is the repr version of the above string, that's why you're seeing \\ here.
But, in fact the actual string contains just '\' not \\.
>>> strs
'C:\\Users\\Josh\\Desktop\\20130216'
>>> s = r"f\o"
>>> s #repr representation
'f\\o'
>>> len(s) #length is 3, as there's only one `'\'`
3
But when you're going to print this string you'll not get '\\' in the output.
>>> print strs
C:\Users\Josh\Desktop\20130216
If you want the string to show '\\' during print then use str.replace:
>>> new_strs = strs.replace('\\','\\\\')
>>> print new_strs
C:\\Users\\Josh\\Desktop\\20130216
repr version will now show \\\\:
>>> new_strs
'C:\\\\Users\\\\Josh\\\\Desktop\\\\20130216'
Let me make it simple and clear. Lets use the re module in python to escape the special characters.
Python script :
import re
s = "C:\Users\Josh\Desktop"
print s
print re.escape(s)
Output :
C:\Users\Josh\Desktop
C:\\Users\\Josh\\Desktop
Explanation :
Now observe that re.escape function on escaping the special chars in the given string we able to add an other backslash before each backslash, and finally the output results in a double backslash, the desired output.
Hope this helps you.
Use escape characters: "full\\path\\here", "\\" and "\\\\"
In python \ (backslash) is used as an escape character. What this means that in places where you wish to insert a special character (such as newline), you would use the backslash and another character (\n for newline)
With your example string you would notice that when you put "C:\Users\Josh\Desktop\20130216" in the repl you will get "C:\\Users\\Josh\\Desktop\x8130216". This is because \2 has a special meaning in a python string. If you wish to specify \ then you need to put two \\ in your string.
"C:\\Users\\Josh\\Desktop\\28130216"
The other option is to notify python that your entire string must NOT use \ as an escape character by pre-pending the string with r
r"C:\Users\Josh\Desktop\20130216"
This is a "raw" string, and very useful in situations where you need to use lots of backslashes such as with regular expression strings.
In case you still wish to replace that single \ with \\ you would then use:
directory = string.replace(r"C:\Users\Josh\Desktop\20130216", "\\", "\\\\")
Notice that I am not using r' in the last two strings above. This is because, when you use the r' form of strings you cannot end that string with a single \
Why can't Python's raw string literals end with a single backslash?
https://pythonconquerstheuniverse.wordpress.com/2008/06/04/gotcha-%E2%80%94-backslashes-are-escape-characters/
Maybe a syntax error in your case,
you may change the line to:
directory = str(r"C:\Users\Josh\Desktop\20130216").replace('\\','\\\\')
which give you the right following output:
C:\\Users\\Josh\\Desktop\\20130216
The backslash indicates a special escape character. Therefore, directory = path_to_directory.replace("\", "\\") would cause Python to think that the first argument to replace didn't end until the starting quotation of the second argument since it understood the ending quotation as an escape character.
directory=path_to_directory.replace("\\","\\\\")
Given the source string, manipulation with os.path might make more sense, but here's a string solution;
>>> s=r"C:\Users\Josh\Desktop\\20130216"
>>> '\\\\'.join(filter(bool, s.split('\\')))
'C:\\\\Users\\\\Josh\\\\Desktop\\\\20130216'
Note that split treats the \\ in the source string as a delimited empty string. Using filter gets rid of those empty strings so join won't double the already doubled backslashes. Unfortunately, if you have 3 or more, they get reduced to doubled backslashes, but I don't think that hurts you in a windows path expression.
You could use
os.path.abspath(path_with_backlash)
it returns the path with \
Use:
string.replace(r"C:\Users\Josh\Desktop\20130216", "\\", "\\")
Escape the \ character.