Unable to search for '\\n' using regular expressions in python3

Question

>>> import re
>>> a='''\\n5
... 8'''
>>> b=re.findall('\\n[0-9]',a)
>>> print(b)
['\n8']

Why does it show \n8 and not \n5? I used a \ in front of \n the first time. I am finding the use of raw string in regex in python a bit confusing. To me it does not seem to be making any changes to the result

score 2 · Answer 1 · answered Jul 09 '17 at 11:21

2

\\n is not a newline, it's an escaped backslash with an n.

>>> import re
>>> a = '''\n5
... 8'''
>>> a=re.findall('\\n[0-9]',a)
>>> print(a)
['\n5', '\n8']

answered Jul 09 '17 at 11:21

rinkert

6,593
2
12
31

score 2 · Accepted Answer · answered Jul 09 '17 at 11:23

2

This is because in strings, the newline character is considered that, a single character.

When you do \\n5 you're escaping the \, so that's literally printing \n5, and not a newline by Python standards.

When you search for a regex such as \\n[0-9] though, in the first \ you're escaping the \n regex expression, so in the end you're looking for \n which is Python's newline. That matches the actual newline in your string, but not \\n which is two separate characters, an escaped \ and an n.

answered Jul 09 '17 at 11:23

Pedro von Hertwig Batista

2,922
1
15
20

How do i get \\n5 in the result? – Vaibhav Jul 09 '17 at 11:31
@VaibhavPandey if you want to get both `\\n5` and `\n8`, you can use a non-capture group to check for one of the two: `'(?:\\n|\\\\n)[0-9]'`. If you just want the `\\n5`, include double escaped slashes: `'\\\\n[0-9]'`. – Pedro von Hertwig Batista Jul 09 '17 at 11:41

score 1 · Answer 3 · answered Jul 09 '17 at 11:19

1

because \\n5 is not valid new line, it will print \n5

answered Jul 09 '17 at 11:19

uingtea

6,002
2
26
40

Unable to search for '\\n' using regular expressions in python3

3 Answers3