Barcode Reader

Barcode Reader


Learning barcode specifications and implementing a barcode reader with Python.

This time I will use EAN-13 (from Wikipedia) .

The input is a String of length 95 representing the barcode. Each databit is displayed by an underscore or space. An underscore is the bar area. The input may be reversed. You should decode the barcode so that the output was a String of length 13.

In case a barcode does not conform to the specifications, return None.

The input final digit is the checksum. It is calculated from the other 12 digits, but in this mission it may be wrong. You must return None for this.


    '_ _   _ __ _  ___ __  __  _  __ ____ _  ___ _ _ _ __  __ __ __  _    _ _ ___  _  ___ _   _  _ _') == '5901234123457'

    '_ _   __ _ _  ___ ____ _   _ __  _ ___  ___ _ _ _ __  __ _  ___ _  ___ _ ___  _  _   _ _    _ _') == '4003994155486'


Input: The image of the barcode is a String of length 95. It consists only of underscores or spaces.

Output: The decoded barcode number is a String of length 13 or None.

How it is used:
understand the mechanism of a barcode.


  • len(barcode) == 95
  • all(b in ('_', ' ') for b in barcode)

Invalid hot key. Each hot key should be unique and valid
Hot keys:
CheckiO Extensions

CheckiO Extensions allow you to use local files to solve missions. More info in a blog post.

In order to install CheckiO client you'll need installed Python (version at least 3.8)

Install CheckiO Client first:

pip3 install checkio_client

Configure your tool

checkio --domain=py config --key=

Sync solutions into your local folder

checkio sync

(in beta testing) Launch local server so your browser can use it and sync solution between local file end extension on the fly. (doesn't work for safari)

checkio serv -d

Alternatevly, you can install Chrome extension or FF addon

checkio install-plugin
checkio install-plugin --ff
checkio install-plugin --chromium

Read more here about other functionality that the checkio client provides. Feel free to submit an issue in case of any difficulties.

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