Modifying escape sequences in strings

[Thomas Philips]

I have been playing around with reading strings with embedded escape
sequences from files both using readline() and codecs.open() and have
a question.I create a file "test.txt" with exactly one line:
1\na\n\n2\n\n3

I then open test.txt and then read it using readline():

input_file=file("test.txt")
x=input_file.readline() x
1\\na\\n\\n2\\n\\n3
print x
1\na\n\n2\n\n3
The readline has escaped the backslashes, so that they print
correctly. I tried to replace the double backslashes with single
backslashes to escape the "n" x.replace("\\","\")
SyntaxError: EOL while scanning single-quoted string

How can I replace the escaped backslash with a backslash? I realize
that I can solve the problem by reading the file using
codecs.open("test.txt","r","string_escape") as suggested by Peter
Otten. I'm trying to do the same thing in different ways to better
understand Python

Sincerely
Thomas Philips

[Larry Bates]

The problem is that the backslash (\) has special
meaning to Python. It means that the next character
is escaped (has special meaning).

Try following:

x=x.replace("\\n","\n")

This works for me.

-Larry
"Thomas Philips" <tk****@hotmail.com> wrote in message
news:b4**************************@posting.google.c om...

I have been playing around with reading strings with embedded escape
sequences from files both using readline() and codecs.open() and have
a question.I create a file "test.txt" with exactly one line:
1\na\n\n2\n\n3

I then open test.txt and then read it using readline():

input_file=file("test.txt")
x=input_file.readline() x
1\\na\\n\\n2\\n\\n3
print x
1\na\n\n2\n\n3
The readline has escaped the backslashes, so that they print
correctly. I tried to replace the double backslashes with single
backslashes to escape the "n" x.replace("\\","\")
SyntaxError: EOL while scanning single-quoted string

How can I replace the escaped backslash with a backslash? I realize
that I can solve the problem by reading the file using
codecs.open("test.txt","r","string_escape") as suggested by Peter
Otten. I'm trying to do the same thing in different ways to better
understand Python

Sincerely
Thomas Philips

[Jeff Epler]

If you want to translate two backslashes into a single backslash,
have to write
x.replace("\\\\", "\\")
the first is a string of length 2 and the second is a string of length
1. I don't know why the tutorial doesn't cover this point explicitly
(http://python.org/doc/current/tut/no...00000000000000)
but the language reference does (http://python.org/doc/current/ref/strings.html)
.... but there are no sequences of two backslashes in the strings you
were working with.

However, I think that referring to "escaped backslashes" in the string
you read shows that there's some other misunderstanding of what is going
on. Is your final goal to turn the backslash-n sequences into actual
newlines, or what? If this is your goal, then you should use the
"string_escape" codec in Python 2.3:

'\\n'.decode("string_escape")

'\n'
This took a string containing backslash-n and returned a string
containing a newline character.

Jeff