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patternpythonMinor

Dynamically generating Strings (or other variables)

Submitted by: @import:stackexchange-codereview··
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dynamicallygeneratingvariablesotherstrings

Problem

I've got a Python script which is meant to launch several other shell scripts with the appropriate setup and parameters. I construct the file paths from other variables so that it's easier to change one setting and have it apply everywhere, rather than hardcoding everything.

So, for example:

HOME_DIRECTORY = os.path.dirname(os.path.realpath(__file__))

ONHAND_ACC_NAME = 'onhand_accuracy'
SHRINK_NAME = 'shrink'
SHELL_SCRIPT_EXTENSION = '.ksh'
CONFIG_FILE_EXTENSION = '.conf'

ONHAND_ACC_SHELL_SCRIPT = HOME_DIRECTORY + '/' + ONHAND_ACC_NAME + SHELL_SCRIPT_EXTENSION
SHRINK_SHELL_SCRIPT = HOME_DIRECTORY + '/' + SHRINK_NAME + SHELL_SCRIPT_EXTENSION
ONHAND_ACC_CONFIG_FILE = HOME_DIRECTORY + '/' + ONHAND_ACC_NAME + CONFIG_FILE_EXTENSION
SHRINK_CONFIG_FILE = HOME_DIRECTORY + '/' + SHRINK_NAME + CONFIG_FILE_EXTENSION


These are all constants defined at the top of the script. (Feel free to tell me a more Pythonic way to do this than constants, as well. I've heard before that "Python should have no constants at all", though I'm not sure how accurate or purist that is.)

In Java, I would do something much cleaner, like use an enum to generate appropriate file paths as needed:

public enum FileType {

    SHELL_SCRIPT   (".ksh"),
    CONFIGURATION  (".conf");

    private static final String HOME_DIRECTORY = "/path/to/scripts";
    private static final String FILE_SEPARATOR = FileSystems.getDefault().getSeparator();

    private final String extension;

    private FileType(String extension) {
        this.extension = extension;
    }

    public String getFilePath(String name) {
        return HOME_DIRECTORY + FILE_SEPARATOR + name + extension;
    }
}


Then I could simply invoke this whenever I wanted to and get a file path, rather than hardcoding them as constants, like so:

FileType.SHELL_SCRIPT.getFilePath("onhand_accuracy");


Any similar tips on how I can improve this practice/technique in Python? I know I could have a similar function in Pyt

Solution

For something similar to your Java solution, you could have this in filetype.py:

import os.path

class FileType(object):
    HOME_DIRECTORY = "/path/to/scripts"

    def __init__(self, extension):
        self.extension = extension

    def file_path(self, name):
        return os.path.join(self.HOME_DIRECTORY, name + self.extension)

SHELL_SCRIPT = FileType(".ksh")
CONFIGURATION = FileType(".conf")


Then the usage would be

import filetype
filetype.SHELL_SCRIPT.file_path("onhand_accuracy")

Code Snippets

import os.path

class FileType(object):
    HOME_DIRECTORY = "/path/to/scripts"

    def __init__(self, extension):
        self.extension = extension

    def file_path(self, name):
        return os.path.join(self.HOME_DIRECTORY, name + self.extension)

SHELL_SCRIPT = FileType(".ksh")
CONFIGURATION = FileType(".conf")
import filetype
filetype.SHELL_SCRIPT.file_path("onhand_accuracy")

Context

StackExchange Code Review Q#45495, answer score: 5

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