Replace values in Depth column of a 2G magnetometer file

replace_2g_depth_column.py

#!/usr/bin/env python3

import argparse

"""
Replace the contents of the column headed "Depth" in a tab-delimited text 
file with a repeated, increasing range of specified numbers. Intended to fix 
incorrect depths in 2G magnetometer files. The column header is retained in 
the output file. The values below it are replaced with a sequence starting at 
the specified min_depth and ending at the specified max_depth (inclusive). 
Depths are specified in centimetres and incremented by 1 cm per line, 
but written in metres (se specifying --min_depth=15, --max_depth=114 will 
produce 0.15, 0.16, ... , 1.13, 1.14). The range will loop back to the start 
if there are more lines in the file than are covered by the range. 

By Pontus Lurcock, 2018. Released into the public domain.
"""


def main():
    parser = argparse.ArgumentParser()
    parser.add_argument("min_depth", type=int)
    parser.add_argument("max_depth", type=int)
    parser.add_argument("infile")
    parser.add_argument("outfile")
    args = parser.parse_args()
    with open(args.infile, newline="") as fh:
        inlines = fh.readlines()
    depth_column = inlines[0].strip().split("\t").index("Depth")
    outlines = [inlines[0]]
    depth = args.min_depth
    for line in inlines[1:]:
        fields = line.split("\t")
        fields[depth_column] = "{:.2f}".format(depth / 100)
        depth += 1
        if depth > args.max_depth:
            depth = args.min_depth
        outlines.append("\t".join(fields))
    with open(args.outfile, "w") as outfh:
        outfh.writelines(outlines)


if __name__ == "__main__":
    main()