re.sub: escaping capture group followed by numeric(s)

[Jon Clements]

Hi All,

(I reckon this is probably a question for MRAB and is not really
Python specific, but anyhow...)

Absolutely basic example: re.sub(r'(\d+)', r'\1', 'string1')

I've been searching around and I'm sure it'll be obvious when it's
pointed out, but how do I use the above to replace 1 with 11?
Obviously I can't use r'\11' because there is no group 11. I know I
can use a function to do it, but it seems to me there must be a way
without. Can I escape r'\11' somehow so that it's group 1 with a '1'
after it (not group 11).

Cheers,

Jon.

 

[MRAB]

Hi All,

(I reckon this is probably a question for MRAB and is not really
Python specific, but anyhow...)

Absolutely basic example: re.sub(r'(\d+)', r'\1', 'string1')

I've been searching around and I'm sure it'll be obvious when it's
pointed out, but how do I use the above to replace 1 with 11?
Obviously I can't use r'\11' because there is no group 11. I know I
can use a function to do it, but it seems to me there must be a way
without. Can I escape r'\11' somehow so that it's group 1 with a '1'
after it (not group 11).

re.sub(r'(\d+)', r'\g<1>', 'string1')

 

[Peter Otten]

(I reckon this is probably a question for MRAB and is not really
Python specific, but anyhow...)

Absolutely basic example: re.sub(r'(\d+)', r'\1', 'string1')

I've been searching around and I'm sure it'll be obvious when it's
pointed out, but how do I use the above to replace 1 with 11?
Obviously I can't use r'\11' because there is no group 11. I know I
can use a function to do it, but it seems to me there must be a way
without. Can I escape r'\11' somehow so that it's group 1 with a '1'
after it (not group 11).

Quoting

http://docs.python.org/library/re.html#re.sub

"""
In addition to character escapes and backreferences as described above,
\g<name> will use the substring matched by the group named name, as defined
by the (?P<name>...) syntax. \g<number> uses the corresponding group number;
\g<2> is therefore equivalent to \2, but isn’t ambiguous in a replacement
such as \g<2>0. \20 would be interpreted as a reference to group 20, not a
reference to group 2 followed by the literal character '0'. The
backreference \g<0> substitutes in the entire substring matched by the RE.
"""

Peter

 

[Jon Clements]

Quoting

http://docs.python.org/library/re.html#re.sub

"""
In addition to character escapes and backreferences as described above,
\g<name> will use the substring matched by the group named name, as defined
by the (?P<name>...) syntax. \g<number> uses the corresponding group number;
\g<2> is therefore equivalent to \2, but isn’t ambiguous in a replacement
such as \g<2>0. \20 would be interpreted as a reference to group 20, not a
reference to group 2 followed by the literal character '0'. The
backreference \g<0> substitutes in the entire substring matched by the RE..
"""

Peter

Thanks Peter and MRAB. I must have been through the docs half a dozen
times and missed that - what a muppet! One of those days I guess...

Cheers,

Jon.