How to append \ character to the start of the string in python, it throws an error saying
SyntaxError: EOL while scanning string literal
I need to append \ whenever underscore is seen in the string
for example:
__x_a → \_\_x_a this needs to be done only for the initial underscores
A single backslash in Python is written like this:
"\\"
Various ways to convince yourself of this:
>>> len("\\")
1
>>> print("\\")
\
>>> "\\\\\\\\\\\\\\\\\\"[0]
'\\'
>>> chr(92)
'\\'
>>> '\N{REVERSE SOLIDUS}'
'\\'
The weirdness is because, since the backslash is the escape character, a backslash itself must be escaped.
So, to answer the question in the title:
How to append “\” to the start of the string in python
You can use:
mystring = "\\" + mystring
In your example case, which is escaping only leading underscores, try something like this:
>>> mystring = '__x_a'
>>> n = next((i for i,c in enumerate(mystring) if c != '_'), len(mystring))
>>> result = mystring.replace('_', r'\_', n)
>>> print(result)
\_\_x_a
You can use re.sub
>>> import re
>>> s = "__x_a"
>>> new_s = re.sub(r'^_*', lambda x: x.group().replace('_', '\_'), s)
>>> print(new_s)
\_\_x_a
