如何在python中注入转义序列

Question

I need to put escape sequences in a string for certain characters (using double quote as an example here). For example, if I have a string abra"cada"bra , I need to generate this: abra\\"cada\\"bra . But if the string is already has escape characters for my interested literals (ie double quote in this example) abra\\"cada\\"bra , I need to leave it alone. What is the easiest way to do it in python?

(The idea is to write it to a text file which is read by another utility.)

Answer 1

首先解码字符串可能最容易，因此没有任何内容被转义，然后重新转义结果字符串。

Answer 2

You can get it with the appropriate negative look behind assertion in regular expressions:

import re

PAT = re.compile(r'(?<!\\)"')
txt1 = '"abra"cada"bra'
txt2 = '\\"abra\\"cada\\"bra'
print PAT.sub(r'\\"', txt1)
print PAT.sub(r'\\"', txt2)

This would make sure, it even works correctly, if the quote is the first character of the sting, as in the example above.

Answer 3

something like this

def esc_string(mystring, delim, esc_char='\\'):
    return (esc_char+delim).join([s[:-1] if s.endswith(esc_char) else s for s in mystring.split(delim)])

then

print esc_string('abra"cada"bra', '"')
abra\"cada\"bra
print esc_string('abra\\"cada\\"bra', '"')
abra\"cada\"bra
print esc_string('"boundary test"', '"')
\"boundary test\"
print esc_string('\\"boundary test\\"', '"')
\"boundary test\"

Answer 4

Assuming \\ has no special meaning other than immediately before certain characters (eg, '"' ) then @chepner's suggestion to unescape first could be implemented as:

def escape(text, char='"', escape="\\"):
    escaped_char = escape + char
    text = text.replace(escaped_char, char) # unescape
    return text.replace(char, escaped_char) # escape

Input

"abra"cada"bra\"
\"abra\"cada\"bra"
"abra\"cada"bra\"
abra\"cada\\"bra\"
abra\"cada\\\"bra\"

Output

\"abra\"cada\"bra\"
\"abra\"cada\"bra\"
\"abra\"cada\"bra\"
abra\"cada\\"bra\"
abra\"cada\\\"bra\"

Answer 5

Regular expressions will do it. This one says to match the " character if it is not preceded by a backslash. I used an 'r' at the front of the strings to tell python not to treat the '\\' character specially and I had to put it in twice to tell the regular expression parser not to use it specially. Try help(re) for what the (?

import re
re.sub(r'(?<!\\)"', r'\"', 'abra"cada\\"bra')
# Returns 'abra\\"cada\\"bra'