Find the default open command by file extension on Windows

main.py

# _*_ coding:utf-8 _*_

from subprocess import Popen, PIPE


class AssociationNotFound(Exception):
    # means: File association not found for extension .ext
    pass


class FileTypeError(Exception):
    # means: File type 'file_type' not found or no open command associated with it.
    pass


def getFileTypeByExtension(extension):
    """
    use `assoc` command to get the file type by extension
    C:\Users\root>assoc .png
    .png=IrfanView.png

    C:\Users\root>assoc .igs
    File association not found for extension .igs

    Args:
        extension <str> file extension, like ".png"
    Raise:
        AssociationNotFound
    Return:
        result <str> file type, like "IrfanView.png"
    """
    p = Popen(["assoc", extension], stdout=PIPE, stderr=PIPE, shell=True)
    output, error = p.communicate()
    if error:
        raise AssociationNotFound(error)
    return output.strip().split("=")[-1]


def getOpenCommandByFileType(file_type):
    """
    use `ftype` command to get the open command by file type
    C:\Users\root>ftype IrfanView.png
    IrfanView.png="<path-to-command>\i_view32.exe" "%1"

    C:\Users\root>ftype pngfile
    File type 'pngfile' not found or no open command associated with it.

    Args:
        file_type <str> file type, like "IrfanView.png"
    Raise:
        FileTypeError
    Return:
        result <str> open command, like '"<path-to-command>\i_view32.exe" "%1"'
    """
    p = Popen(["ftype", file_type], stdout=PIPE, stderr=PIPE, shell=True)
    output, error = p.communicate()
    if error:
        raise FileTypeError(error)
    return output.strip().split("=")[-1]