Suppose I want to change the blue dog and blue cat wore blue hats to the gray dog and gray cat wore blue hats.
With sed I could accomplish this as follows:
$ echo 'the blue dog and blue cat wore blue hats' | sed 's/blue \(dog\|cat\)/gray \1/g'
How can I do a similar replacement in Python? I've tried:
>>> import re
>>> s = "the blue dog and blue cat wore blue hats"
>>> p = re.compile(r"blue (dog|cat)")
>>> p.sub('gray \1',s)
'the gray \x01 and gray \x01 wore blue hats'
You need to escape your backslash:
p.sub('gray \\1', s)
alternatively you can use a raw string as you already did for the regex:
p.sub(r'gray \1', s)
sed syntax.
As I was looking for a similar answer; but wanting using named groups within the replace, I thought I'd add the code for others:
p = re.compile(r'blue (?P<animal>dog|cat)')
p.sub(r'gray \g<animal>',s)
Off topic, For numbered capture groups:
#/usr/bin/env python
import re
re.sub(
pattern=r'(\d)(\w+)',
repl='word: \\2, digit: \\1',
string='1asdf'
)
word: asdf, digit: 1
Python uses literal backslash, plus one-based-index to do numbered capture group replacements, as shown in this example. So \1, entered as '\\1', references the first capture group (\d), and \2 the second captured group.
group1 is 1 can we replace group1 to lets say 5 so the final output can be something like 5asdf. (i.e., replacing the entire group)
1 at all, in that case simply don't capture it (by not enclosing it in parenthesis). If you want to extract strings with regex, use re.match or re.search (and variants), that will give you for example a group dict (docs.python.org/3/library/re.html#re.Match.groupdict) and you can format/parse data from there as you likefunction public xyzname() and I wanted to change public to private so only way I can do it by grouping function and xyzname() and applying something like \\1 private \\2, but I was wondering if I can group just public as group 1 and replace it with private, is it possible?\\1 private \\2 and adjust it as necessaryTry this:
p.sub('gray \g<1>',s)
\g is not a valid escaped code. The safe way of writing your code should still be: p.sub('gray \\g<1>',s)
\g was chosen especifically not to clash with other escape codes. It would've been a poor choice by Python devs if it did. docs.python.org/2/library/re.html#re.sub
p.sub(r'gray \g<1>',s) to prevent the `` being parsed by Python, allowing it to be sent directly to the regex engine.