Python regex and replace with incremented number

Question

I have a file which contains in it several lines of problematic syntax, I'd like to do find all occurrences of it and replace it with acceptable syntax.

Example:

<field id="someId" type="xs:decimal" bind="someId">
    <description/>
    <region id="Calc.R_315.`0" page="1"/>
    <region id="Calc.R_315.`1" page="1"/>
</field>

I'd like to a string replacement of all occurrences of

<dot><tick><number> i.e. .`0 or .`1 or .`2 et cetera

with

<dash><number> i.e. -1 or -2 or -3

Notice it begins at 1 instead of 0.

I have the following python code which performs an inline replacement of however it starts at 0, I'd like it to start at 1.

with fileinput.input(files="file.xml", inplace=True, backup='.original.bak', mode='r') as f:
    for line in f:
        pattern = "\.`(\d+)"
        result = re.sub(pattern, lambda exp: "-{}".format(exp.groups()[0]), line)
        print(result, end='')

How to accomplish my goal?

Why doesn't adding 1 to the argument in the format() function work? — pault
– pault, Commented Feb 6, 2018 at 17:12

nisemonoxide · Accepted Answer · 2018-02-06 17:52:44Z

8

You are almost at the solution yourself!

The only thing remaining is to convert the captured number into an int, and add 1 to it. Simple!

So the relevant line of code becomes:

result = re.sub(pattern, lambda exp: "-{}".format(int(exp.groups()[0]) + 1), line)

Another slight modification that can be made is to change .groups()[0] to .group(1). You can learn more about group and its usage in the documentation.

One last thing: It is always better to define your regex pattern as a raw string so as to avoid any future headaches.

edited Feb 6, 2018 at 17:52

answered Feb 6, 2018 at 17:24

nisemonoxide

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Ajax1234 · Accepted Answer · 2018-02-06 17:14:06Z

3

You can try this:

import re
s = """
<field id="someId" type="xs:decimal" bind="someId">
   <description/>
   <region id="Calc.R_315.`0" page="1"/>
   <region id="Calc.R_315.`1" page="1"/>
</field>
"""
new_s = re.sub('\.`\d+', '{}', s).format(*map(lambda x:'-{}'.format(int(x)+1), re.findall('(?<=\.`)\d+(?=")', s)))
print(new_s)

Output:

<field id="someId" type="xs:decimal" bind="someId">
  <description/>
  <region id="Calc.R_315-1" page="1"/>
  <region id="Calc.R_315-2" page="1"/>
</field>

answered Feb 6, 2018 at 17:14

Ajax1234

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