CODEWITHSUNDEEP
pythonflat-file
Denis
Denis

Reputation: 1555

fixed length flat file without separators

I have a comprehension question not related to any particular language, but since I am writing in python, I tagged python. I am asked to provide some data in "fixed length, flatfile without separators". It confuses me, since I understand it like:

Input: Column A: date (len6)

Input: Column B: name (len20)

Output: "20170409MYVERYSHORTNAME[space][space][space][space][space]"

"MYVERYSHORTNAME" is only 15 char long, but since it's fixed 20-length output, I am supposed to fill 5 times it with something ? It's not specified.

Why do someone even needs a file without separators? He/she will need to break it down to separated fields anyway, what's the point?

Upvotes: 0

Views: 263

Answers (2)

Guillaume
Guillaume

Reputation: 6009

This kind of flat (binary) file is meant to be faster/easier to read by machines, and more memory efficient than the equivalent in a more human friendly representation (eg, JSON, CSV, etc.). For example, the machine can preallocate the appropriate amount of memory before reading the contents. Nowadays, with the virtually unlimited quantity of RAM and dynamic nature of the languages, nobody uses flat files anymore (unless it is specifically needed).

In Python, in order to deal properly with this kind of binary files, you can for example use the struct module from the standard library: https://docs.python.org/3.6/library/struct.html#module-struct

Example:

import struct
from datetime import datetime
mydate = datetime.now()
myshortname = "HelloWorld!"

struct.pack("8s20s", mydate.strftime('%Y%m%d').encode(), myshortname.encode())

>>> b'201709HelloWorld!\x00\x00\x00\x00\x00\x00\x00\x00\x00'

Upvotes: 1

Chris Adams
Chris Adams

Reputation: 1097

Typically, when you see fixed-length files, you're dealing with legacy systems. The AS400, for instance, usually spits out fixed-length files with artificial separators (why, I don't know, but that's what I've seen).

Usually, strings are right-padded with spaces, and numbers are left-padded with 0's (zeros).

This is not absolute.

Upvotes: 1

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