How can I use "number placeholders" when using .replace()?

Question

I have a file which has multiple instances of "position": [num, num] (num is a random number).

Now I want to replace those instances with "position": [num, num, 0], so basically just add a , 0 after the two numbers. But how can I do that?

I tried doing text.replace('"position": [%d, %d]', '"position": [%d, %d, 0]'). That didn’t work though.

Asked By: LiQ

||

Source

Answer 1

You can use the following re.sub to do the replacements (demo).

Edit for OP’s comments:

Given that the file is fairly small, I’d iterate through it while reading, applying the substitution as I go, and then dump all the subbed lines into the same location.

import re

file_path = "/tmp/74987707.txt"  # substitute your own

output_lines = []

with open(file_path, mode="rt") as f:
    for line in f:
        subbed_line = re.sub(
            r'("position": [d+(?:.?d*), d+(?:.?d*))(])',
            r'1, 02',
            line
            )
        output_lines.append(subbed_line)

with open(file_path, mode="wt") as f:
    f.writelines(output_lines)

Regex explanation:

group 1 ("position": [d+(?:.?d*), d+(?:.?d*))

( start
"position": [ match exactly (escaping [)
d+ match one or more digit
(?:.?d*) non capturing group, match a possible literal dot . and one or more digits
, match exactly
d+(?:.?d*) see above
) end

group 2 (])

( start
] match exactly (escaping ])
) end

Answered By: ljmc

Answer 2

From the structure of what you posted it looks like a json file, you can just loop through the items and append 0

import json

with open('example.json', 'r') as f:
    data = json.load(f)

for item in data:
    if 'position' in item:
        if isinstance(item['position'], list) and len(item['position']) == 2:
            item['position'].append(0)

with open('example_modified.json', 'w') as f:
    json.dump(data, f)

Answered By: Joe S

How can I use "number placeholders" when using .replace()?

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