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
Related
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!)
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 am creating a program that automatically generates my reports in LaTeX, where I have to escape special LaTeX characters. Basically, whenever I read $ or _ or %, etc, I have to replace it by \$, \_ and \%, respectively.
I naively tried to do mystring.replace('$','\$'), yet it adds a double backslash, as shown below:
my_text_to_parse = "$x^2+2\cdot x + 2 = 0$"
my_text_to_parse.replace('$','\$')
#=> "\\$x^2+2\cdot x + 2 = 0\\$"
Is there any way to avoid doubling escape characters?
You're seeing the double backslash because you're getting the representation of the string, not the output. In the representation, it prints an backslash because \ is a protected character and therefore must be escaped. This is because it is used in special characters (e.g. \t, \n) and usage might be confused.. When the string is actually printed or saved, those double backslashes should be printed properly as a single backslash.
For example, compare
print('\')
# SyntaxError: EOL while scanning string literal
to
print('\\')
# \
In the first string, the second quotation mark is being escaped by the backslash. This shows why you generally can't use raw backslashes in strings. In the second string, the second backslash is being escaped by the first. The two backslashes get interpreted as a single one.
print(repr('\\'))
# '\\'
But the representation of the second string still shows both backslashes. This behavior is the same as other special characters such as \n, where it can be a bit easier to see the issue. Just as \n is the special character that means line break, \\ is the special character that means single backslash.
print('hi\nmom')
# hi
# mom
print(repr('hi\nmom'))
# 'hi\nmom'
To actually answer your question, the way you're doing it should work properly, but you probably don't want to do it quite that way. This is because creating a string with '\$' doesn't make this escaping issue clear. It seems like it is a special character \$ in the same way that \n is a special character, but because there is no character defined like that, the python interpreter is smart enough to replace the single backslash with a double backslash. But you generally don't want to rely on that behavior.
A better way to do it is to explicitly escape the backslash with another one or to use a raw string, where no escaping is allowed. All of these will give the same result.
s = '$x^2+2\\cdot x + 2 = 0$'
print(s.replace('$', '\$')) # Technically works, but not as clear
# \$x^2+2\cdot x + 2 = 0\$
print(s.replace('$', '\\$')) # Escaping the backslash
# \$x^2+2\cdot x + 2 = 0\$
print(s.replace('$', r'\$')) # Using a raw string
# \$x^2+2\cdot x + 2 = 0\$
print re.sub(r"\$","\$",x)
You can try re.sub.It will give the expected result.
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 - '\\'.
I don't know why i can't find it, but i wanted to replace the special character '\' in python.
I have a String within i have '\' characters but i confident find the solution, to replace it with '-'.
This is what happening while i am trying to replace,
>>> x = 'hello\world'
>>> x
'hello\\world'
>>> x.replace('\', '-')
File "<stdin>", line 1
x.replace('\', '-')
SyntaxError: EOL while scanning string literal
EDIT:
Do try this it in the eclipse IDLE
x = 'hello\world'
print x
x.replace('\\', '-')
print x
Output:
hello\world
hello\world
You need to escape it with another backslash:
x.replace('\\', '-')
Backslashes are special, in that they are used to introduce non-printing characters like newlines into a string.
It's also how you add a ' character to a '-quoted string, which is what Python thinks you were trying to do. It sees \' and interprets as a literal quote within the string, rather than letting the ' end the string. Then it gets to the end of the string and finds EOL ("end of line") before the end of the string.
To introduce a real backslash, you need to double it. You can see that Python itself did this when printing the representation of your initial string here:
>>> x
'hello\\world'
Note the double backslash.
You ought to use a double backslash when specifying your string in the first place. The reason that doesn't need it is that \w is not a special character, so it gets interpreted as a literal backslash and a w. Had you said 'Hello\now' you would have a string with a newline in it.
You could have also marked the string as a "raw" string by prepending it with r as in r'hello\world'. This marks the string as not being eligible for any substitutions of special characters.
According to docs:
The backslash (\) character is used to escape characters that
otherwise have a special meaning, such as newline, backslash itself,
or the quote character.
You need to escape backslash with another backslash:
x.replace('\\', '-')
This \' is interpreted as a special character. Escape it:
x.replace('\\', '-')
in python your string
x = 'hello\world'
is replaced as x = "hello\world"
so to achieve u have to write
x.replace('\\','-')