如何使用正则表达式在单引号之间查找双引号？

Question

I have a string like "how "are" you", I want to replace quotes which are inside the quotes surrounding "are" with \" using regex in python

input_file =  'D:/Extracts/yourFileName.csv'
file_output= 'D:/Extracts/yourFileName_out.csv'

with open(input_file, 'r',encoding="utf8") as f, open(file_output, 'w',encoding="utf8") as fo:
    for line in f:
        fo.write(line.replace('"', '\"').replace(""", ""))

I want the output like "how \"are\" you"

Answer 1

The strings '\"' and '"' are identical: they both are just a single double-quote, because the sequence \" encodes a double-quote character (usually for use in " -quoted strings).

If you really want a backslash before the quote, you'll have to escape it:

fo.write(line.replace('"', '\\"'))

In order to not replace the first and last character, you can instead use regular expressions:

fo.write(re.sub('(?<!^)"(?!$)', '\\"', line))

The regular expression consists of a negative lookbehind ( (?<!^) ; asserting that no line starts before the quote), the quote character itself, and a negative lookahead ( (?!$) ; asserting that no line ends after the quote).

Demo