How to replace "\" with "\\" in python(type string)? I tried line = line.replace("\", "\\"), but it gives error SyntaxError: unexpected character after line continuation character
In Python strings, \ is an escape, meaning something like, "do something special with the next character." The proper way of specifying \ itself is with two of them:
line = line.replace("\\", "\\\\")
Funny enough, I had to do the same thing to your post to get it to format properly.
To replace \ with \\ in a Python string, you must write \\ in the Python string literal for each \ you want. Therefore:
line = line.replace("\\", "\\\\")
You can often use raw strings to avoid needing the double backslashes, but not in this case: r"\" is a syntax error, because the r modifier doesn't do what most people think it does. (It means both the backspace and the following character are included in the resulting string, so r"\" is actually a backslash followed by a quote, and the literal has no terminating quote!)
Related
I have a password. It contains newline (lets for now omit why) character and is:
"h2sdf\ndfGd"
This password is in dict my_dict. When I just print values of dict I get "\" instead of "" - "h2sdf\ndfGd"! Don't understand why.
When I get it and use it to authenticate to web server, it says that Authentication fails. When I try to compare:
my_dict["password"] == "h2sdf\ndfGd"
it returns False.
But when I try just print(my_dict["password"]) I get h2sdf\ndfGd which is identical, but for python it is not. Why? I am lost.
Check this:
>>> print("h2sdf\ndfGd")
h2sdf
dfGd
>>> print("h2sdf\\ndfGd")
h2sdf\ndfGd
You simply have to escape \n with a double \ backslash, to prevent it to become a newline.
Characters like tabs, newlines, which cannot be represented in a string are described using an escape sequence with a backslash.
In order to indicate that the backslash is not part of an escape sequence(\n, \t, ...), it must itself be escaped using another backslash: \\.
my_dict["password"] == "h2sdf\\ndfGd"
If you don't want to have to escape all your \, you can use a raw string instead.
Raw strings are prefixed with r or R, and treat backslashes \ as literal characters.
my_dict["password"] == r"h2sdf\ndfGd"
I have the following Python code:
localExtractpath = "D:\Python\From 0 to 1\Excel\"
if os.path.exists(localZipPath):
print("Cool! '" + localZipPath + "' exists...proceeding...")
This gives me the error:
File "", line 2
localExtractpath = "D:\Python\From 0 to 1\Excel\"
^
SyntaxError: EOL while scanning string literal
When I escape the last \ in the string, the code works. Why do I only have to escape the last \?
Why do I only have to escape the last \?
Because only after the last \ there is a symbol (") which together with \ forms an escape sequence — \" (escaping the role of the quote symbol " as a string terminator).
If \ with subsequent symbol(s) don't form an escape sequence, it's kept as is, i.e. as the backslash symbol itself.
(In your case neither \P, nor \F and nor \E form an allowed escape sequence, so the symbol \ itself is interpreted literally — as is.)
An (unsolicited) solution:
Use forward slashes (/) instead of backslashes (\)
(all Windows system calls accept them, too):
localExtractpath = "D:/Python/From 0 to 1/Excel/"
The last backslash in "D:\Python\From 0 to 1\Excel\" is escaping your ending quotation mark, so in the eyes of the interpreter, your string is unterminated. In fact, you have to escape all your backslashes if you want to use the literal backslash in your string:
"D:\\Python\\From 0 to 1\\Excel\\"
Other answers are right: you should escape all your backslashes and, even better, you should use forward slash for path elements (you can even take a look at the pathlib library).
But to answer specifically your question on why the issue lies only in the last one and not in the previous backslashes, you should take a look at the definition of string literals.
You will see that there is a (short) list of characters for which the backslash makes something particular. For the rest, the backslash is taken as itself.
For instance "\n" is interpreted not as a string with two characters (\ and n) but as a string with only a single line-feed character.
That is not the case with "\P", "\F" or "\E" which are two characters each since they don't have a specific meaning.
\" and \' are particular in that they allow to respectively insert a " or ' character in a string literal delimited by this same character.
For example, 'single: \', double "' and "single: ', double: \"" are two ways to define the single: ', double " string literal.
buf= 'b"\\\x00\\\x00\\\x1a\\\x00/H\\\x00\\\x00\\\xf8f\\\x14'""'
I need:
buf= 'b"\x00\x00\x1a\x00/H\x00\x00\xf8f \x14'""'
I tried: buf=buf.replace("\\","\")
But I am getting error: SyntaxError: EOL while scanning string literal
Make sure to escape each backslash with another backslash:
buf=buf.replace("\\\\","\\")
Or, you can use raw strings:
buf=buf.replace(r"\\",r"\")
You have to escape \ with a \. So replacing \ becomes \\ and replacing \\ becomes \\\\
buf= 'b"\\x00\\x00\\x1a\\x00/H\\x00\\x00\\xf8f\\x14'""
buf=buf.replace("\\\\","\\") # give b"\x00\x00\x1a\x00/H\x00\x00\xf8f\x14
in your code
buf=buf.replace("\\","\")
the first backslash will consider as an escape-sequence and will read the next character with special meaning. so in this stage "\" it will skip the second " so it will raise
SyntaxError: EOL while scanning string literal
replace your code with
buf=buf.replace(r"\\",r"\")
here 'r' is used to read the string completely,it will skip/avoid the escape sequances
I know this is a noob question, but new to Python and trying to understand the following:
Why does the backslash escape work without error here:
>>> print "this is \\\ a string"
this is \\ a string
But when I try:
>>> print "\\\"
I get:
SyntaxError: EOL while scanning string literal
The first backslash escapes the second backslash, and the third escapes the double quote, which then fails to terminate the string. You need either print "\\\\" or print "\\\"", depending on what output you are actually trying to get. (The first will print \\ and the second will print \".)
Your first \ escapes your second \. Now the third \ waits for escaping another character but instead gets ' and escapes it. That's why it shows this error. This is the same error you will get if you try to do this
>>> print 'abc # Line ended while scanning string
In this case
>>> print "this is \\\ a string"
The third \ gets a space character which is not a special character. Hence third \ does not escape anything and is the part of the string.
When you do :
print "\\\"
First \ covers the second one and third one covers the " (quote itself). So its like python does not see the ending quotes , so you get the errror.
Just a further note on what has already been mentioned, each time you use a backslash it consumes the character following it. As you probably know, some have special meaning such as \t would insert a tab character. As you've seen, \\ is designed to show the backslash.
What Python also lets you do is prefix any string with r which is used to mean disable the escape mechanism inside the string. For example in your first example, adding the r would display all three backslashes 'as is'.
print r"this is \\\ a string"
this is \\\ a string
But be warned, even this trick will fail if you try your second example. You still need to avoid a backslash in the last character of a string:
print r"\\\"
SyntaxError: EOL while scanning string literal
It is because you have three backslashes , so the first two backslash indicate an escaped backslash , and the next backslash is used to escape the quotes, and hence there are no real ending quotes for your string causing the issue.
In the first string, the third backslash does not escape anything as it appears before a space which is not a special character and hence it gets printed.
If you do -
print "\\\ "
it may work (worked for me in python 3.4)
My version -
>>> print("\\\ ")
\\
Without space -
>>> print("\\\")
File "<stdin>", line 1
print("\\\")
^
SyntaxError: EOL while scanning string literal
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 - '\\'.