Parsing file input into variables in python

Question

I have a text file called input.txt with the following contents:

landmark {
  x: 0.48397088050842285
  y: 0.25201746821403503
  z: -0.285147100687027
  visibility: 0.9999984502792358
}
landmark {
  x: 0.4912211298942566
  y: 0.23858927190303802
  z: -0.27364951372146606
  visibility: 0.9999926090240479
}
landmark {
  x: 0.4947235584259033
  y: 0.23917287588119507
  z: -0.27369818091392517
  visibility: 0.9999934434890747
}

How do I write a function that puts each value into a list of lists? For example: list[0] = {0.48397,0.252017,-0.28514,0.999999} list [1] = {0.491221,0.2385892,-0.27364,0.999992} and so on..

What format is this in? Your best bet would be to find a library that parses that format, rather than you writing the parsing yourself. — ndc85430
– ndc85430, Commented Jan 1, 2023 at 7:37
Agreed, your best bet it to get the exact format of your source. But if it always comes like this you could write a small parser. — Yonas Kassa
– Yonas Kassa, Commented Jan 1, 2023 at 7:42

Chris · Accepted Answer · 2023-01-01 07:53:07Z

1

Assuming the format doesn't deviate, a very naive approach would be a whole bunch of regex substitutions to turn this into what it looks like: a list of dictionaries, and then ast.literal_eval it. A trailing comma I haven't addressed actually wraps this up a single element tuple, hence the [0].

import ast
import re

ast.literal_eval(
  re.sub(r'(\d)\s', r'\1,', 
  re.sub(r'\}\s*landmark\s*{', '},{', 
  re.sub(r'$', ',', 
  re.sub(r'\}\s*\Z', '}]', 
  re.sub(r'\Alandmark\s*\{', '[{', 
  re.sub(r'([a-zA-Z]+):', r'"\1":', s))))))
)[0]

answered Jan 1, 2023 at 7:53

Chris

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Surjit Samra · Accepted Answer · 2023-01-01 08:18:49Z

Here is my approach without regx

s = """landmark {
  x: 0.48397088050842285
  y: 0.25201746821403503
  z: -0.285147100687027
  visibility: 0.9999984502792358
}
landmark {
  x: 0.4912211298942566
  y: 0.23858927190303802
  z: -0.27364951372146606
  visibility: 0.9999926090240479
}
landmark {
  x: 0.4947235584259033
  y: 0.23917287588119507
  z: -0.27369818091392517
  visibility: 0.9999934434890747
}"""
d= [i.replace('{\n','').replace('}\n','').replace('\n',',').replace(',}','') for i in s.split('landmark') if i]
t = [i.replace('x','"x"').replace('z','"z"').replace('visibility','"k"').replace('y','"y"').replace('k','visibility') for i in d]
[eval('{'+i+'}').values() for  i in t ]
#Your output: 
[dict_values([0.48397088050842285, 0.25201746821403503, -0.285147100687027, 0.9999984502792358]),
 dict_values([0.4912211298942566, 0.23858927190303802, -0.27364951372146606, 0.9999926090240479]),
 dict_values([0.4947235584259033, 0.23917287588119507, -0.27369818091392517, 0.9999934434890747])]

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