Read fixed width text file in Python

app.py

import struct
from operator import itemgetter
from pathlib import Path


def get_struct_unpacker(fieldspecs, istart, iwidth):
    """
    Build the format string for struct.unpack to use, based on the fieldspecs.
    fieldspecs is a list of [name, start, width] arrays.
    Returns a string like "6s2s3s7x7s4x9s".
    """
    unpack_len = 0
    unpack_fmt = ""
    for fieldspec in fieldspecs:
        start = fieldspec[istart] - 1
        end = start + fieldspec[iwidth]
        if start > unpack_len:
            unpack_fmt += str(start - unpack_len) + "x"
        unpack_fmt += str(end - start) + "s"
        unpack_len = end
    struct_unpacker = struct.Struct(unpack_fmt).unpack_from
    return struct_unpacker


fieldspecs = [
    # Name, Start, Width, Type
    ["ID", 1, 6, int],
    ["NAME", 9, 14, str],
    ["Twitter", 24, 13, str]
]
iname, istart, iwidth, itype = 0, 1, 2, 3  # field indexes

fieldspecs.sort(key=itemgetter(istart))
struct_unpacker = get_struct_unpacker(fieldspecs, istart, iwidth)
field_indices = range(len(fieldspecs))

data = []

for line in Path('./data.txt').open():
    raw_fields = struct_unpacker(line.encode())  # split line into field values
    line_data = {}
    for i in field_indices:
        fieldspec = fieldspecs[i]
        fieldname = fieldspec[iname]
        cast = fieldspec[itype]
        value = cast(raw_fields[i].decode().strip())
        line_data[fieldname] = value
    data.append(line_data)

print(data)

data.txt

123456  Bruno Rocha    @rochacbruno 
456789  Rodolfo Viana  @rodolfoviana

output.sh

[{'ID': 123456, 'NAME': 'Bruno Rocha', 'Twitter': '@rochacbruno'}, {'ID': 456789, 'NAME': 'Rodolfo Viana', 'Twitter': '@rodolfoviana'}]

muito bom!

Nice work. I would like to use your code to search a fixed width file that have up to 10,0000 rows of records. I want to enter a search string at the prompt and have the script return records from specific locations on a line or record line.
Is there a way to read specific line of record in the file? Let's say I want to read a record at line 110 or extract a value from position 129 on line 110?
Thank you.
Fulton

New to Python but Like to see how to take this result and Insert into MSSQL table. I have file with over 1600 columns which I can get start point and width and if this code can read my question is what should I do or use in order to insert into a table. TIA