What is the regular expression for finding line ending with '\'(backslash) in Python?

Quote:

But it's not working.

Is not help us to understand what you want.

Quote:

I want to print the line number of the line which ends with backslash in python

Try

for Line in fp:
    if (re.search('(\\)', Line)):
         print(LineNumber)
    LineNumber += 1
    continue

Quote:

want to merge the line till Linenumber which contains '\' + 1

This is another problem.
you need to have this in a string instead of an array:

Hi
Hello \
Good Morning \
All
Programmers

Something like

test= "Hi\nHello \\\nGood Morning \\\nAll\nProgrammers"

then a RegEx that will match

"Hello \\\nGood Morning \\\nAll"

once you got the match in a single string, replace the "\\\n"

Just a few interesting links to help building and debugging RegEx.
Here is a link to RegEx documentation:
perlre - perldoc.perl.org[^]
Here is links to tools to help build RegEx and debug them:
.NET Regex Tester - Regex Storm[^]
Expresso Regular Expression Tool[^]
RegExr: Learn, Build, & Test RegEx[^]
Online regex tester and debugger: PHP, PCRE, Python, Golang and JavaScript[^]
This one show you the RegEx as a nice graph which is really helpful to understand what is doing a RegEx:
Debuggex: Online visual regex tester. JavaScript, Python, and PCRE.[^]
This site also show the Regex in a nice graph but can't test what match the RegEx:
Regexper[^]