i would like to create a string in the following exact format :
"\"\"\"\nThis is a beautiful world.\n"
But the code :
test ="\"\"\"\nthis is a beautiful world.\n"
test
gives the output :
'"""\nthis is a beautiful world.'
please help in getting an exact text.
My string test should look exactly like the string it has been initialized to. but after initialization, it actually gives the output as mentioned. i want to concatenate the test string to another string
the symbol "\" is called an escape character in most programming languages. this is used to add symbols to a string that might not be easy to add. eg - to add a double quote into a string, we add the \" to the string. eg -
a = "he said, \"hello\" to me"
this would give the output as -
he said "hello" to me
here, the "\" acts as a symbol for the code which allows it to recognize characters which might raise errors other-wise.
to include a backslash in your code, add an extra backslash to it. eg -
a = "\\"
here, the value of a is \.
if you still haven't been able to understand it, try - this tutorial
for your code,try this -
test = "\\\"\\\"\\\"\\nThis is a beautiful world.\\n"
and if you also want the double quotes at the ends,
test = "\"\\\"\\\"\\\"\\nThis is a beautiful world.\\n\""
The first thing to note is, that just typing in the variable name when running python interactively returns the canonical string representation of the object and not (necessarily) the plain value of the object.
For strings this means (among other things) that quotes are added around the output (in your example the outermost single quotes) and any newlines are replaced with "\n".
This means that, although your output does show "\n" the actual string contains a newline character in its place.
The check what a string looks like, you should use the print() function to, well, print it.
>>> test = "\"\"\"\nthis is a beautiful world."
>>> test
'"""\nthis is a beautiful world.'
>>> print(test)
"""
this is a beautiful world.
>>>
Also, when running the code from a file, lines just containing variable names will not result in any output.
To answer the question
There are a few ways to handle that.
Assuming that the desired output is
"""\nThis is a beautiful world.\n
i.e. the outermost double quotes are not supposed to be part of the string, that is
While using double quotes ("…") to denote strings: escape any \ or " by prepending it with \:
>>> test ="\\\"\\\"\\\"\\nthis is a beautiful world.\\n"
>>> print(test)
\"\"\"\nthis is a beautiful world.\n
Within regular strings \ is used to designate control character. For example: \n is interpreted as newline, \b would be a backspace. If you need to have a \ in a string, you need actually write two \\.
If you are usually using "…" for string notation, this allows for a more consistent coding style but it is (especially in this case) quite ugly and might be hard to understand at a glance.
As your string contains a lot of " characters, just use single quotes ('…') to designate the string. This removes the need to escape ":
>>> test = '\\"\\"\\"\\nthis is a beautiful world.\\n'
>>> print(test)
\"\"\"\nthis is a beautiful world.\n
This is less consistent (if "…" is usually used for strings, but allows the code to be quite a bit closer to the desired output.
Use raw strings (r'…' or r"…") to disable the interpretation of control characters and allow the use of " within the string:
>>> test = r'\"\"\"\nthis is a beautiful world.\n'
>>> print(test)
\"\"\"\nthis is a beautiful world.\n"
or even
>>> test = r"\"\"\"\nthis is a beautiful world.\n"
>>> print(test)
\"\"\"\nthis is a beautiful world.\n"
This allows the code to be identical to the desired output, but it has some limitations when it comes to freely mixing " and ' within a single string as it is not possible to escape the quotation marks within the string without also adding \ to the string output. This can be seen in the second example, where we use \" to escape the double quote within r"…" in the code but where the \s are still present in the output. While this works well in this specific case, I would recommend against using \' within r'…' or \" within r"…" to avoid confusion.
Related
I have a string looks like this:
(The whole code block is a string, aka, this string contains quotation marks.)
"he\"llo", "world\n", "fro,m"
[update] Aka, the "actual" string is this:
"\"he\\\"llo\", \"world\\n\", \"fro,m\""
I want to get an array of strings like this:
[ "\"he\\\"llo\"", "\"world\\n\"", "\"fro,m\"" ]
[update] Comma inside quotation marks should be remained.
In my opinion, there are several ways to solve this:
build a automata (DFA or NFA) for this syntax
using several status flags like inQuote, handle judging logics with lots of if else
write a complex but clever Regular Expression for this
Are there any general solutions to this problem? Or how should I actually do using those thinkings above?
P.S. It couldn't be better if some syntax errors like "unclosed quotation mark" can be found.
You need to first define your grammar. This is a simple grammar for your case:
document = *WS [string *WS *(',' *WS string *WS)]
string = %x22 *char %x22
char = %x20-21 / %x23-5B / escape / %x5D-10FFFF
escape = %x5C (%x5C / %x22 / 't' / 'n' / 'r')
WS = %x9 / %x20
You can read it as:
A document may begin/end with a white space, then may have one or more strings separated by commas. Before and after each comma there may be some white space.
A string is made of characters and begins and ends with double quotes Unicode/ASCII hex code 22.
Each character (char), may be: 1) any non control Unicode character before the double quotes i.e. hex 20 (space) or hex 21 (exclamation mark); 2) any character after the double quotes and before the escape slash \ (hex 5C); 3) an escape character sequence; 4) any other Unicode character after the slash (hex 5C).
The escape sequence (rule escape) begins with the escape slash \ and is followed by another slash, or the characters t for tab, n for line feed and r for carriage return. You may add and other escapable characters if you want, as for a C++ string syntax you can see here: https://en.cppreference.com/w/cpp/language/escape .
A white space (WS) is a tab or space, you may add and %xA and %xD for line feed and carriage return respectively.
By the use of this grammar you will get this tree for your input:
The screenshort is from the Tunnel Grammar Studio online laboratory that can run ABNF grammars (as the one above), and I work on.
After you have the grammar, you may use tools to generate a parser, or you can write one yourself. If you want to do it by hand (preferable for so small and simple grammar), you may have one function per each grammar rule that reads one character and checks is it the expected one. If your input finishes when you are parsing the string rule, then you have an input with a started but not finished string.
Your actual string syntax tree will look like that:
I'm having a bit of an issue trying to do an ascii art challenge in GS, since it requires you finishing a line with the \ symbol.
The problem is that "\"p breaks the program since it thinks you escaped a quote, and "\\"p prints two backslashes. I've tried string concatenation, removing one character at a time, printing substrings, etcetc - Nothing seems to work!
I need this string to be printed out, so how would this be done?
It seems that the behavior with p is buggy. I'll look for a place to report it.
However, "\\" by itself does not print two backslashes; it prints one.
Here's a test link to prove it.
Output:
\
"\\" creates a string with 1 backslash because strings are escaped. This is the same as languages like Ruby.
p escapes strings, so a string with one backslash will be displayed as two. This is also the same as languages like Ruby.
So if you want to print a single backslash, or print things without the quotes, you need to print unescaped strings. The best way to do this is with implicit IO (anything on the stack that is left over is printed unescaped).
The program
"\\"
Should print
\
You could also use print or puts if you don't want to use implicit IO.
Sorry, this is likely a simple solution. In a server response, I am trying to return an emoji. Right now, I have this line:
return [b"Hello World " “👋”.encode(“utf-8”)]
However, I get the following error:
return [b"Hello World " “�👋”.encode(“utf-8”)]
^
SyntaxError: invalid character in identifier
What I'd like to see is: Hello World 👋
The problem is that a byte string b'...' cannot contain a character which does not fit into a byte. But you don't need a byte string here anyway; encode will convert a string to bytes - that's what it does.
Try
return ["Hello World “👋”".encode("utf-8")]
The quotes in your question were wacky; I assume you want curly quotes around the emoji and honest-to-GvR quotes around the Python string literals.
In Python, you can put (almost) any Unicode character in a string literal.
Also, you can use most Unicode letters in identifiers, eg. if you think it's appropriate to define a variable α (Greek lower-case alpha).
But you can't use "fancy quotes" for delimiting string literals.
Look carefully: the double quotes around the emoji (and also around utf-8) aren't straight ASCII quotes, but rather typographical ones – the ones word processors substitute when typing a double quote in text.
Make sure you use a proper programming editor or an IDE for coding.
Then the line will look like this:
return [b"Hello World " "👋".encode("utf-8")]
Edit:
I realise that this still doesn't work: you cannot mix byte string and Unicode string literals (even though here the Unicode literal gets converted to bytes later).
Instead, you have to concatenate them with the + operator:
return [b"Hello World " + "👋".encode("utf-8")]
Or use a single string literal, like tripleee suggested.
There are several problems. Your code:
return [b"Hello World " “👋”.encode(“utf-8”)]
You see, you are using “ and ” twice, instead of the proper double quote character ("). You should use a proper code editor, or disable character conversion. You should care also on copy and paste.
As you see from the error, the problem is not the emoji on the string, but a problem of identifier (and it is a syntax error), so unknown characters outside string.
But if you correct to:
return [b"Hello World " "👋".encode("utf-8")]
you still have an error: SyntaxError: cannot mix bytes and nonbytes literals.
This because Python will merge strings before to call the function encode, but one is a b-string and the other it is a normal string.
So you could use one of the following:
return [b"Hello World " + "👋".encode("utf-8")] # this force order of operator
or the following two (that are equivalent).
return [b"Hello World " "👋"]
return [b"Hello World 👋"]
Python3 uses UTF-8 as default source encoding, so your editor will already encode the emoji into UTF-8, so you can use it in a b-string (UTF-8 encoded).
Note: this is not a very safe assumption: one could manually force source code to be in other encodings, but in that case, you will have probably also problem with the first method (saving a file with emoji in other encodings).
Please note, that the question is similar like this one, but still different so that those answers won't solve my problem:
For insertion of control characters like e.g. \x08, it seems that I have to use double quotes ".
All spaces needs to be preserved exactly as given. For line breaks I use explicitly \n.
I have some string data which I need to store in YAML, e.g.:
" This is my quite long string data "
"This is my quite long string data"
"This_is_my_quite_long_string_data"
"Sting data\nwhich\x08contains control characters"
and need it in YAML as something like this:
Key: " This is my" +
" quite long " +
" string data "
This is no problem as long as I stay on a single line, but I don't know how to put the string content to multiple lines.
YAML block scalar styles (>, |) won't help here, because they don't allow escaping and they even do some whitespace stripping, newline / space substitution which is useless for my case.
Looks that the only way seems to be using double quoting " and backslashes \, like this:
Key: "\
This is \
my quite \
long string data\
"
Trying this in YAML online parser results in "This is my quite long string data" as expected.
But it unfortunately fail if one of the "sub-lines" has leading space, like this:
Key: "\
This is \
my quite\
long st\
ring data\
"
This results in "This is my quitelong string data", removed the space between the words quite and long of this example. The only thing that comes to my mind to solve that, is to replace the first leading space of each sub-line by \x20 like this:
Key: "\
This is \
my quite\
\x20long st\
ring data\
"
As I'd chosen YAML to have a best possible human readable format, I find that \x20 a bit ugly solution. Maybe someone know a better approach?
For keeping human readable, I also don't want to use !!binary for this.
Instead of \x20, you can simply escape the first non-indentation space on the line:
Key: "\
This is \
my quite\
\ long st\
ring data\
"
This works with multiple spaces, you only need to escape the first one.
You are right in your observation that control characters can only be represented in double quoted scalars.
However the parser doesn't fail if the sub-lines (in YAML speak: continuation lines) have a leading space. It is your interpretation of the YAML standard that is incorrect. The standard explicitly states that for multi-line double quoted scalars:
All leading and trailing white space characters are excluded from the content.
So you can put as many spaces as you want before long as you want, it will not make a difference.
The representer for double quoted scalars for Python (both in ruamel.yaml and PyYAML) always does represent newlines as \n. I am not aware of YAML representers in other languages where you have more control over this (and e.g. get double newlines to represent \n in your double quoted scalars). So you probably have to write your own representer.
While writing a representer you can try to make the line breaking be smart, in that it minimizes the number of escaped spaces (by putting them between words on the same line). But especially on strings with a high double space to word ratio, combined with a small width to operate in, it will be hard (if not impossible) to do without escaped spaces.
Such a representer should IMO first check if double quoting is necessary (i.e. there are control characters apart from newlines). If not, and there are newlines you are probably better of representing the string a block style literal scalar (for which spaces at the beginning or end of line are not excluded).
While running an R-plugin in SPSS, I receive a Windows path string as input e.g.
'C:\Users\mhermans\somefile.csv'
I would like to use that path in subsequent R code, but then the slashes need to be replaced with forward slashes, otherwise R interprets it as escapes (eg. "\U used without hex digits" errors).
I have however not been able to find a function that can replace the backslashes with foward slashes or double escape them. All those functions assume those characters are escaped.
So, is there something along the lines of:
>gsub('\\', '/', 'C:\Users\mhermans')
C:/Users/mhermans
You can try to use the 'allowEscapes' argument in scan()
X=scan(what="character",allowEscapes=F)
C:\Users\mhermans\somefile.csv
print(X)
[1] "C:\\Users\\mhermans\\somefile.csv"
As of version 4.0, introduced in April 2020, R provides a syntax for specifying raw strings. The string in the example can be written as:
path <- r"(C:\Users\mhermans\somefile.csv)"
From ?Quotes:
Raw character constants are also available using a syntax similar to the one used in C++: r"(...)" with ... any character sequence, except that it must not contain the closing sequence )". The delimiter pairs [] and {} can also be used, and R can be used in place of r. For additional flexibility, a number of dashes can be placed between the opening quote and the opening delimiter, as long as the same number of dashes appear between the closing delimiter and the closing quote.
First you need to get it assigned to a name:
pathname <- 'C:\\Users\\mhermans\\somefile.csv'
Notice that in order to get it into a name vector you needed to double them all, which gives a hint about how you could use regex. Actually, if you read it in from a text file, then R will do all the doubling for you. Mind you it not really doubling the backslashes. It is being stored as a single backslash, but it's being displayed like that and needs to be input like that from the console. Otherwise the R interpreter tries (and often fails) to turn it into a special character. And to compound the problem, regex uses the backslash as an escape as well. So to detect an escape with grep or sub or gsub you need to quadruple the backslashes
gsub("\\\\", "/", pathname)
# [1] "C:/Users/mhermans/somefile.csv"
You needed to doubly "double" the backslashes. The first of each couple of \'s is to signal to the grep machine that what next comes is a literal.
Consider:
nchar("\\A")
# returns `[1] 2`
If file E:\Data\junk.txt contains the following text (without quotes): C:\Users\mhermans\somefile.csv
You may get a warning with the following statement, but it will work:
texinp <- readLines("E:\\Data\\junk.txt")
If file E:\Data\junk.txt contains the following text (with quotes): "C:\Users\mhermans\somefile.csv"
The above readlines statement might also give you a warning, but will now contain:
"\"C:\Users\mhermans\somefile.csv\""
So, to get what you want, make sure there aren't quotes in the incoming file, and use:
texinp <- suppressWarnings(readLines("E:\\Data\\junk.txt"))