Extract data from textfile in python

Question

I need to write a python function that reads and stores values from a textfile that looks as follows:

I need to store the variables ncols, nrows….. until NODATA_value, and stop there. So only the first 6 lines are needed. Any tips?

I use np.loadtxt to store the matrix occuring after those 6 lines. I know how to read line by line but i want the function to skip those spaces btw the varible name and the value — JustANoob, Jun 13 '19 at 13:14
Can you actually post the text of the file in a code block instead of a screenshot? Are those tabs or spaces? — Zhenhir, Jun 13 '19 at 13:18

score 2 · Answer 1 · answered Jun 13 '19 at 13:22

2

Hi this is very simple to do. I recommend you to see a python tutorial. Anyway this can be a start point.:

width open("myfile.txt") as f:
  for idx,line in enumerate(f):
    if idx>=6: break
    #dostuff

answered Jun 13 '19 at 13:22

Simone

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1
6

score 1 · Answer 2 · answered Jun 13 '19 at 13:14

I'm sure there are many nice libraries that will do this for you, but it's basic Python to do this without learning new libraries. You can put the contents of the folder into a list: How to read a file line-by-line into a list?

From there, it's easy. Use list.index(element) to find the index of 'ncols', and the index of its value is list.index('ncols')+1. https://www.programiz.com/python-programming/methods/list/index

You could use slicing to crop the list off at NODATA_value: Understanding slice notation

score 1 · Accepted Answer · answered Jun 13 '19 at 13:20

You could try something like this:

variables = dict()
with open('my_text_file.txt', 'r') as textfile:
    while True:    
        next_line = textfile.readline()
        if len(next_line) == 0:
            break

        key, value = next_line.split()
        if key == 'NODATA_value':
            break

        variables[key] = value

This assumes that each line in your file is a key-value pair, where the key and value are separated by some amount of whitespace.

The loop will terminate when the end of the file is reached, or when the NODATA_value key is encountered.

Extract data from textfile in python

3 Answers3