如何从txt文件中提取值

Question

I have data fine data.txt:

#  data1     data2      data3        W =    10.251 kg
  -5.827  0.0000E+00  0.0000E+00
  -5.817  0.6202E-03  0.2067E-05
  -5.807  0.2481E-02  0.1654E-04
  -5.797  0.5582E-02  0.5582E-04
  -5.787  0.9924E-02  0.1323E-03

How to make python extract the value of W as weight = 10.251

I used this

W_txt = np.loadtxt('./data.txt',max_rows =1, dtype=np.str, comments = 'c')

weight_txt = W_txt[8]
 
weight = weight_txt.astype(np.float)
print(weight)

but it comes with warning:

DeprecationWarning: `np.float` is a deprecated alias for the builtin `float`. To silence this warning, use `float` by itself. Doing this will not modify any behavior and is safe. If you specifically wanted the numpy scalar type, use `np.float64` here.

Answer 1

Do you know how to read a file in python? If not you can find plenty of tutorials online. It seems like your file is arranged in columns delimited by a tab sign. Furtermore it looks like in the last column you have your wanted value. You can split a tab-delimited spring with "some\ttab-delimited\tstring".split("\t") to get a list with the resulting fragments.

It is not clear how your file is structured. From the looks, it could be your_string = "data1\tdata2\tdata3\tW =\t10.251 kg" . If you manage to parse the data from the file and furthermore want to extract 10.251 from the first line and re-format it to output weight = 10.251 the code would look as following:

with open("/path/to/your/file.txt", "r") as f:
    data = f.readlines()

# get first line
first_line = data[0]

# split string by tab, select last fragment, split again by ' kg' and select first fragment
desired_value = first_line.split("\t")[-1].split(" kg")[0]

# convert to float (optional)
desired_value = float(desired_value)

print("weight: " + desired_value)

I just saw that you updated your code and use numpy - without having your input-data, i imagine you want something like

data = np.loadtxt("mercurial.ini", max_rows=1, dtype=np.str, comments="c").item(0)
value = data.split("\t")[-1].split(" kg")[0]
print("weight: " + value)

You might have to play around with the split parameters if your string is not tab-delimited etc.

Answer 2

If you print that W_txt after reading it, you would see

['#' 'data1' 'data2' 'data3' 'W' '=' '10.251' 'kg']

You're trying to read data at index 8, which doesn't exist. You should read weight data using

weight_txt = W_txt[6]

As for those warnings, as it says, np.float is deprecated, use float instead:

weight = weight_txt.astype(float)

So, the whole code should look like this:

import numpy as np


W_txt = np.loadtxt('./data.txt', max_rows=1, dtype=str, comments='c')

weight_txt = W_txt[6]

weight = weight_txt.astype(float)
print(weight)