如何使用Python将文本文件中的某些文本行放入列表中？

Question

If I have hundreds of these in a text file;

<Vertex> 0 {
  -10.6272 8.71309 10.8633
  <UV> { 0.724203 0.210816 }
  <RGBA> { 0.916 0.609 0.439 1 }
}

How can I get Python to go through the text file and put the second line; -10.6272 8.71309 10.8633 ; of each <Vertex> tag into a list?

Answer 1

You can do it with a regular expression:

>>> import re
>>> r = re.compile("^<Vertex>\s*\d+\s*{\s*([-\d. ]+)", re.MULTILINE)
>>> with open("filename") as fd:
>>>     matches = r.findall(fd.read())
>>> matches
['-10.6272 8.71309 10.8633', '-10.6272 8.71309 10.8633', ...]

Answer 2

catch = False
mylist = []
with open("myfile.txt", "r") as f:
    content = f.readlines()
for line in content:
    if line.startswith("<Vertex>"):
        catch = True
        continue
    if catch:
        catch = False
        mylist.append(line)

This should work.

Answer 3

If you aren't worried about the consistency of the file, then it's pretty easy.

def readFile(path):
    f = open(path, 'r')
    return f.readlines()

def parseVertexes(lines):
    coordinates = []

    for index, line in enumerate(lines):
        if index % 5 == 1: #second line in vertex
            coordinates.append(line.split(" "))

I haven't fully tested, but that should work. You'll have to build up more infrastructure to handle cases if the file isn't consistent.

Answer 4

Assuming your file is like so:

<Vertex> 0 {
  -10.6272 8.71309 10.8633
  <UV> { 0.724203 0.210816 }
  <RGBA> { 0.916 0.609 0.439 1 }
}
<Vertex> 0 {
  -10.6272 8.71309 10.8633
  <UV> { 0.724203 0.210816 }
  <RGBA> { 0.916 0.609 0.439 1 }
}
<Vertex> 0 {
  -10.6272 8.71309 10.8633
  <UV> { 0.724203 0.210816 }
  <RGBA> { 0.916 0.609 0.439 1 }
}

Then you can just start on the second line, and pick every 5th line, using string slicing to get rid of the spaces at the start, and the new line character at the end.

file = open("file.txt","r")
mylist = []
for l,line in enumerate(file):
    if (l - 1) % 5 == 0:
        mylist.append(line[2:-2])

file.close()

Or, as a one liner:

[line[2:-2] for l,line in enumerate(open("file.txt","r")) if (l - 1) % 5 == 0]