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Python assign "\" to a variable [duplicate]

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 - '\\'.

Understanding file locations in python - unexpected errors

I am learning python 3.3 in windows 7. I have a two text files - lines.txt and raven.txt in a folder. Both contain the same text for the first example.
When I try to access ravens, using the code below, I get the error -
OSError: [Errno 22] Invalid argument: 'C:\\Python\raven.txt'
I know that the above error can be fixed by using an escape character like this -
C:\\Python\\raven.txt
C:\Python\\raven.txt
Why do both methods work ? Strangely, when I access lines.txt in the same folder, I get no error ! Why ?
import re
def main():
print('')
fh = open('C:\Python\lines.txt')
for line in fh:
if re.search('(Len|Neverm)ore', line):
print(line, end = '')
if __name__ == '__main__':main()
Also, when I use the line below, I get a completely different error - TypeError: embedded NUL character. Why ?
fh = open('C:\Python\Exercise Files\09 Regexes\raven.txt')
I can rectify this by using \ before every \ in the file path.

\r is an escape character, but \l is not. So, lines is interpreted as lines while raven is interpreted as aven, since \r is escaped.
In [1]: len('\l')
Out[1]: 2
In [2]: len('\r')
Out[2]: 1
You should always escape backslashes with \\. In cases your string doesn't have quotes, you can also use raw strings:
In [9]: len(r'\r')
Out[9]: 2
In [10]: r'\r'
Out[10]: '\\r'
See: https://docs.python.org/3/reference/lexical_analysis.html

maybe you can use raw string.
just like this open(r'C:\Python\Exercise Files\09 Regexes\raven.txt').
When an r' orR' prefix is present, backslashes are still used to
quote the following character, but all backslashes are left in the
string. For example, the string literal r"\n" consists of two
characters: a backslash and a lowercase `n'. String quotes can be
escaped with a backslash, but the backslash remains in the string; for
example, r"\"" is a valid string literal consisting of two characters:
a backslash and a double quote; r"\" is not a value string literal
(even a raw string cannot end in an odd number of backslashes).
Specifically, a raw string cannot end in a single backslash (since the
backslash would escape the following quote character). Note also that
a single backslash followed by a newline is interpreted as those two
characters as part of the string, not as a line continuation.

You can actually use forward slashes instead of backward ones, that way you don't have to escape them at all, which would save you a lot of headaches. Like this: 'C:/Python/raven.txt', I can guarantee that it works on Windows.

Replace \\ with \ in python [duplicate]

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.

python replace single backslash with double backslash [duplicate]

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.

Adding "\" to a String Python | How to insert a "\" before each paren in a string?

How would I add the "\" char to a string?
For instance, if I have "testme" and I do
"testme"+"\"
I would get an error.
What is a "pythonic" approach for adding a "\" before each paren in a string?
For instance to go from "(hi)" to "\(hi\)"
My current approach is to iterate through each char and try to append a "\" which I feel isn't that "pythonic"

Backslashes are used for escaping various characters, so to include a literal backslash in your string you need to use "\\", for example:
>>> print "testme" + "\\"
testme\
So to add a backslash before each paren in a string you could use the following:
s = s.replace('(', '\\(').replace(')', '\\)')
Or with regular expressions:
import re
s = re.sub(r'([()])', r'\\\1', s)
Note that you can also use a raw string literal by adding a the letter r before the opening quote, this makes it so that backslash is interpreted literally and no escaping is done. So r'foo\bar' would be the same as 'foo\\bar'. So you could rewrite the first approach like the following:
s = s.replace('(', r'\(').replace(')', r'\)')
Note that even in raw string literals you can use a backslash to escape the quotation mark used for the string literal, so r'we\'re' is the same as 'we\'re' or "we're". This is why raw string literals don't work well when you want the final character to be a backslash, for example r'testme\' (this will be a syntax error because the string literal is never closed).

>>> import re
>>> strs = "(hi)"
>>> re.sub(r'([()])',r'\\\g<0>',strs)
'\\(hi\\)'
"\" is invalid because you're escaping the closing quote here, so python will raise EOF error.
So you must escape the \ first using another \:
>>> "\\"
'\\'
>>> "\"
File "<ipython-input-23-bdc6fd40f381>", line 1
"\"
^
SyntaxError: EOL while scanning string literal
>>>