This question already has answers here:
Why can't Python's raw string literals end with a single backslash?
(14 answers)
Python Literal r'\' Not Accepted [duplicate]
(5 answers)
Closed 9 years ago.
I was under the impression that in Python a raw string, written as r'this is a raw string' would omit any escape characters, and print EXACTLY what is between the quotes. My problem is that when I try print r'\' I get SyntaxError: EOL while scanning string literal. print r'\n' correctly prints \n, though.
Quoting the documentation:
When an 'r' or 'R' prefix is present, a character following a backslash is included in the string without change, and 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 valid 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).
Added emphasis mine.
Raw strings thus do attach some meaning to a backslash, but only where quotes are concerned.
From the Python docs:
If we make the string literal a “raw” string, \n sequences are not converted to newlines, but the backslash at the end of the line, and the newline character in the source, are both included in the string as data.
You have the wrong idea about raw strings.
Related
This question already has answers here:
What exactly do "u" and "r" string prefixes do, and what are raw string literals?
(7 answers)
Closed 6 years ago.
I first saw it used in building regular expressions across multiple lines as a method argument to re.compile(), so I assumed that r stands for RegEx.
For example:
regex = re.compile(
r'^[A-Z]'
r'[A-Z0-9-]'
r'[A-Z]$', re.IGNORECASE
)
So what does r mean in this case? Why do we need it?
The r means that the string is to be treated as a raw string, which means all escape codes will be ignored.
For an example:
'\n' will be treated as a newline character, while r'\n' will be treated as the characters \ followed by n.
When an 'r' or 'R' prefix is present,
a character following a backslash is
included in the string without change,
and 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 valid 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.
Source: Python string literals
It means that escapes won’t be translated. For example:
r'\n'
is a string with a backslash followed by the letter n. (Without the r it would be a newline.)
b does stand for byte-string and is used in Python 3, where strings are Unicode by default. In Python 2.x strings were byte-strings by default and you’d use u to indicate Unicode.
This question already has answers here:
Can't escape the backslash with regex?
(7 answers)
Closed 7 years ago.
This explanation is from the python documentation:
Both string and bytes literals may optionally be prefixed with a letter 'r' or 'R'; such strings are called raw strings and treat backslashes as literal characters. As a result, in string literals, '\U' and '\u' escapes in raw strings are not treated specially. Given that Python 2.x’s raw unicode literals behave differently than Python 3.x’s the 'ur' syntax is not supported.
If raw strings treat backslashes as char literals, why does the backslash need to be escaped in the expression:
re.compile(r"'\\'")
Instead of just being able to write:
re.compile(r"'\'")
To capture a single backslash when using the re module?
because '\' has special meaning in re it means escape the character after it in the language you use to define a re so if you want to match '+' as a character your re will be '\+'
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 years ago.
How do i escape \n in a string in python.
How do i write out to stdin in python this string "abc\ndef" as one single input
Sys.stdout.write("abc\ndef")
current output
import sys
>>> sys.stdout.write("abc\ndef")
abc
def
I would like it to be abc\ndef
You should escape the backslash so that it's not treated as escaping character itself:
Sys.stdout.write("abc\\ndef")
Background
The backslash \ tells the parser that the next character is something special and must be treated differently. That's why \n will not print as \n but as a newline. But how do we write a backslash then? We need to escape it, too, resulting in \\ for a single backslash and \\n for the output \n.
Docs here, also see this SO question
Alternatively you can use "raw" strings, i.e. prefixing your strings with an r, to disable interpreting escape sequences is your strings:
Sys.stdout.write(r"abc\ndef")
As an alternative to escaping the backslash, you can disable backslash-escaping entirely by using a raw string literal:
>>> print(r"abc\ndef")
abc\ndef
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 8 years ago.
I program in Python in PyCharm and whenever I write '\' as a string it says that the following statements do nothing. For example:
Is there a way to fix this and make it work?
Thanks.
You need to double the backslash:
'/-\\'
as a single backslash has special meaning in a Python string as the start of an escape sequence. A double \\ results in the string containing a single backslash:
>>> print '/-\\'
/-\
If the backslash is not the last character in the string, you could use a r'' raw string as well:
>>> print r'\-/'
\-/
You need to scape them to be in the string, for example:
>>>s='\\'
>>>print s
\
You can also use the r (raw string) modifier in front of the string to include them easily but they can't end with an odd number of backslash. You can read more about string literals on the docs.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
why can’t I end a raw string with a \
Given r'\\' is equivalent to '\\\\', why r'\' isn't equivalent to '\\'?
What I got on my python3.2 was
print(r'\')
File "<stdin>", line 1
print(r'\')
^
SyntaxError: EOL while scanning string literal
You cannot have a backslash as the last character in a raw string unless it is part of an even number of backslashes; it escapes the closing quote.
Compare this to:
>>> r'\ '
'\\ '
From the string literal documentation:
When an 'r' or 'R' prefix is present, a character following a backslash is included in the string without change, and 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 valid 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).