Can I get a technical explanation on the following error

[grocery_stocker]

How come something like '\' causes an error? Here is what I mean.

[cdalten@localhost ~]$ python
Python 2.6.2 (r262:71600, May 3 2009, 17:04:44)
[GCC 4.1.1 20061011 (Red Hat 4.1.1-30)] on linux2
Type "help", "copyright", "credits" or "license" for more information. File "<stdin>", line 1
print "test \"
^
SyntaxError: EOL while scanning string literal
I mean, isn't the '\' a character just like the letter 't'?

 

[Hans Müller]

Try this:

print "\\"

\ is the escape character, it masks the meaning of the next chararcter.

If you write print "\" python tries to print " (the meaning of " as
the string delimiter is beeing masked) and finds no closing "
This is why you got the error.

hth.

Greetings
Hans

 

[DasIch]

'\' starts a escape sequence. You need to escape '\' with a '\' to make it
work. test \

 

[grocery_stocker]

Try this:

print "\\"

\ is the escape character, it masks the meaning of the next chararcter.

If you write print "\" python tries to print " (the meaning of " as
the string delimiter is beeing masked) and finds no closing "
This is why you got the error.

So something like

"\"

changes the meaning of " ? How? Does it just shift the ASCII bit(s)?

 

[Chris Rebert]

So something like

"\"

changes the meaning of " ? How? Does it just shift the ASCII bit(s)?

No, the Python parser handles it when it parses string literals.

Cheers,
Chris

 

[Dennis Lee Bieber]

changes the meaning of " ? How? Does it just shift the ASCII bit(s)?

It does nothing to " itself... What the combination \" tells the
parser is "remove this slash and treat the following quote as part of
the string data and not as a syntax delimiter"
Traceback ( File "<interactive input>", line 1
print "\"
^
SyntaxError: EOL while scanning single-quoted string"

That was ', ", '
Traceback ( File "<interactive input>", line 1
print '\'
^
SyntaxError: EOL while scanning single-quoted string--
Wulfraed Dennis Lee Bieber KD6MOG
(e-mail address removed) (e-mail address removed)
HTTP://wlfraed.home.netcom.com/
(Bestiaria Support Staff: (e-mail address removed))
HTTP://www.bestiaria.com/

 

[Rhodri James]

So something like

"\"

changes the meaning of " ? How? Does it just shift the ASCII bit(s)?

No. There is a fixed set of "escape sequences" as they're called.
The Fine Manual lists them here:

http://docs.python.org/reference/lexical_analysis.html#literals

 

[Jim Garrison]

And as an interesting exercise, try

print r'test \'
print r'test \\'

Because of the way raw string parsing is defined, neither of these will
pass the parser. In fact, a raw string cannot have a backslash as
its last character.

 

[Niklas Norrthon]

And as an interesting exercise, try

print r'test \'
print r'test \\'

Because of the way raw string parsing is defined, neither of these will
pass the parser.  In fact, a raw string cannot have a backslash as
its last character.

Tried it:SyntaxError: EOL while scanning string literal
'test \\\\'

Second one is accepted. See the language reference section 2.4.1 as of
why; http://www.python.org/doc/current/r...is.html?highlight=raw strings#string-literals

/Niklas Norrthon

 

[pdpi]

How come something like '\'  causes an error? Here is what I mean.

[cdalten@localhost ~]$ python
Python 2.6.2 (r262:71600, May  3 2009, 17:04:44)
[GCC 4.1.1 20061011 (Red Hat 4.1.1-30)] on linux2
Type "help", "copyright", "credits" or "license" for more information.>>> print "test \"

  File "<stdin>", line 1
    print "test \"
                 ^
SyntaxError: EOL while scanning string literal



I mean, isn't the '\' a character just like the letter 't'?

Ask yourself: 'How would I tell Python to print the " character when
it's used as the string delimitation character?'. Unlike us (you
probably didn't even blink at the usage of ' in "it's" versus its
usage as quote delimiters in that sentence), computers can't quite
tell usage from context. So you have to come up with a way to express
ourselves. Many languages use the \ character as an escape character,
which modifies the meaning of the next character in a string. \n, \t,
\" are all common. Other languages use other conventions -- I program
ABAP professionally, and it uses ' as the string delimiter, and '' as
a literal -- so a string with one single ' is expressed as ''''.

The python interpreter isn't doing any bit magic here, it's just
reading a \ character followed by a " character and changing its
interpretation of " appropriately.

 

[Piet van Oostrum]

JG> And as an interesting exercise, try
JG> print r'test \'
JG> print r'test \\'

JG> Because of the way raw string parsing is defined, neither of these will
JG> pass the parser. In fact, a raw string cannot have a backslash as
JG> its last character.

Cannot have an odd number of backslashes as its last characters.
test \\