如何将字符串转换为数字列表

Question

I have a problem of converting list from string to numbers in Python.

I read a file and need to extract the coordinate data from it.

The file contains these coordinates:

(-5 -0.005 -5)
(-4.9 -0.005 -5)
(-4.8 -0.005 -5)
(-4.7 -0.005 -5)
(-4.6 -0.005 -5)
(-4.5 -0.005 -5)
(-4.4 -0.005 -5)
(-4.3 -0.005 -5)
(-4.2 -0.005 -5)
(-4.1 -0.005 -5)

First, I read the file and get the coordinates using this code:

f = open("text.txt", 'r')
if f.mode == 'r':
    contents = f.readlines()

After that, if i called contents[0], it showed (-5 -0.005 -5) as a string.

I tried manipulating the contents.

coor = contents[0]                  # picking 1 list of coordinates
allNumber = coor[1:-2]              # delete the open and close brackets
print(list(map(int, allNumber)))    # hopefully get the integers mapped into x, y, and z coordinates :(

I got results like this:

ValueError: invalid literal for int() with base 10: '-'

I want something like [-5, -0.005, -5] so I can extract each number inside it.

Answer 1

You can do it like this:

with open('test.txt') as f:
    lines = (line.strip()[1:-1] for line in f)
    values = (tuple(map(float, line.split())) for line in lines)
    data = list(values)

print(data)
# [(-5.0, -0.005, -5.0), (-4.9, -0.005, -5.0), (-4.8, -0.005, -5.0),
#  (-4.7, -0.005, -5.0), (-4.6, -0.005, -5.0), (-4.5, -0.005, -5.0),
#  (-4.4, -0.005, -5.0), (-4.3, -0.005, -5.0), (-4.2, -0.005, -5.0), (-4.1, -0.005, -5.0)]

Use with open()... to make sure that the file gets closed whatever happens.

lines is a generator, it iterates on the lines of the file and yields each line stripped of the newline, after cutting the first and last character, the parenthesis.

values generate a tuple for each of these cleaned lines, by splitting it and turning the values to floats, as they aren't all integers.

We then make a list out of it.

Answer 2

data = []
with open('test.txt') as f:  # Better way to work with files
    lines = f.readlines()

for line in lines:
    data.append(line.strip()[1:-1].split(", "))

after that data will be list of lists, so you can get any element with data[index_of_the_line][index of the elemnt]