Formatting raw string in Python when using exact match regex

Question

The fr prefix can combine f and r flag.
But when it comes to the regex's exact match, it seems that it can't format the raw string well:

import re

RE1 = r'123'
RE2 = re.compile(fr'@{3} {RE1}')

Then, the RE2.pattern will become '@3 123',

but what I want is '@{3} 123'.

What is your intended meaning for @{3}? Is the 3 a placeholder, or is this literal text? — Tim Biegeleisen
– Tim Biegeleisen, Commented Mar 6, 2019 at 3:48
@TimBiegeleisen the @{3} means exact match @ 3 times here, 3 is not a placeholder. — funkid
– funkid, Commented Mar 6, 2019 at 4:23

Allan · Accepted Answer · 2019-03-06 04:10:43Z

3

You have to escape the braces surrounding the 3 like this, otherwise they will be interpreted as string interpolation:

import re

RE1 = r'123'
RE2 = re.compile(fr'@{{3}} {RE1}')
print(RE2)

This produces:

@{3} 123

Ref: https://www.python.org/dev/peps/pep-0498/

Note that the correct way to have a literal brace appear in the resulting string value is to double the brace:
>>> f'{{ {4*10} }}'
'{ 40 }'
>>> f'{{{4*10}}}'
'{40}'

edited Mar 6, 2019 at 4:10

answered Mar 6, 2019 at 4:07

Allan

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Comments

hd1 · Accepted Answer · 2019-03-06 03:56:02Z

0

RE2 = re.compile(r'@{3} '+RE1)

Works for me, observe:

RE2.pattern

'@{3} 123'

Hope that helps.

answered Mar 6, 2019 at 3:56

hd1

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