Skip to main content

Simple boilerplate for cli scripts

Project description

fissle - Quick command line interfaces

Create a semi-self-documenting command line interface that handles loading configuration files and enabling env variable overloading in addition to command line arguments by defining a simple schema of the configuration and a class with your "business logic".

Example: this is a minimal required setup for having configurations and a command line interface ready for use:

from fissle import c, NamedTuple

class C(NamedTuple):
   a: int = 1
class Cli:
    def foo(self):
        # using configuration

In other words, use this to wrap your scripts as command line commands without fussing about and maintaining argument parsing and duplicating comments for help or remembering what the arguments were and did while still having the typical use experience of a cli program (e.g. --help, subcommands, ...). This implementation is focused on a premise that for a simple script you have a global configuration which would be used through out the user code i.e. a context for the program. That configuration is populated with given arguments falling back on defaults in the code and some further complimentary options.

Should work for linux, macos and windows.


pip install --user fissle

See alternative options at the end of the README


See the example file in tester/ Here's a run down of the individual parts in it.

First import the required components:

from fissle import c, NamedTuple

In your code define the schema as a NamedTuple decorating it with c:

class Configuration(NamedTuple):
    a: str = 'A'  # a description
    x: int = 1  # x description

"Configuration" is an arbitrary name, no magic there. The inherited NamedTuple simplifies the schema's templating to defining just the attributes (i.e. a and x in this example). Those have a set way:

    # attribute: type = default value  # Description for the --help
    a: str = 'A'  # a description

a is the attribute which can be called in the code later with c.a. It has a type of 'str', default value of 'A'. The comment after it is parsed for the command line so it's not redundant. All of these parts will be parsed for the '--help' for the subcommands of the cli, which should be defined as follows:

class Cli:
    def subcommand_foo(self):
        """This will be shown in --help for subcommand-foo"""

    def subcommand_bar(self):
        """This will be shown in --help for subcommand-bar"""

The methods are parsed as subcommands for the cli and their respective doc strings will show in the subcommands' help print out. Note the usage of the parsed configuration c:


Also, to enable autocompletion in IDEs, this hack is needed for the time being:

c: Configuration = c

Put it in the "global space" e.g. just after defining the template. See the tester/ for a specific example.

When all is complete, the imported c variable should have all the bits and pieces for the configuration. It can be used inside the Cli class as well as imported around the codebase thus encapsulating all the configurations into one container with quick access with attributes c.a, c.x, etc...

Running the cli

# Test the damage (presuming you did the flit step below)
tester -- -h
tester subcommand-foo -- -h
tester subcommand-bar

Output should resemble this (fire v0.1.3 prints out Args, fire v0.2.1 doesn't (though looks much nicer))

$ tester subcommand-foo -- -h

Type:        method
String form: <bound method Cli.subcommand_foo of <__main__.Cli object at 0x000002995AD74BE0>>
File:        C:\Users\foobar\code\py\fissle\tester\
Line:        18
Docstring:   This will be shown in --help for subcommand-foo
    --a (str): a description (Default is 'A')
    --x (int): x description (Default is 1)

Usage: subcommand-foo [--X ...]

Configuration file and environment variables

The c decorator/configuration chains multiple configuration options together in order of priority (lower number overrides higher number):

  1. command line arguments
  2. Environment variables
  3. configuration file definitions
  4. defaults in the schema/template/namedtuple class

The configuration file should be named with postfix .cfg e.g. foo.cfg and have an ini type formatting with a 'Default' section:

# foo.cfg
x = 2

The keys are the same as what you define in the schema. You can define all, some or none of the attributes. Same applies for the env variables.

# linux example
X=2 tester subcommand-foo

Installing as command line program i.e. a command

# Install dev version (omit --symlink for more permanent solution):
flit install --symlink

Out-of-the-box features via Fire

See the Python Fire's Flags documentation for nice additional features such as:

# e.g. is our cli program subcommand-foo -- --trace -- --interactive -- --completion

Why another cli framework?

This is just a tool to slap together a cli program in python, so you don't have to resort to bash. The intention is to get something reasonably configurable and generic up and running as fast as possible. I can't bother to memorize argparses syntax, even though it's a very good package. Also click works nice for more elaborate things though fire is my personal favourite for the time being.

Installing from source

Note: If you prefer some other tooling, maybe try out DepHell to transform this from pipenv to requirements.txt etc.. (or what ever floats you boat)


# From the beginning...
pip install -U pip pipenv

# on some mac configurations, when pipenv isn't included in the path..
sudo -H pip install -U pip pipenv

pipenv environment

pipenv install --ignore-pipfile

# activate the environment alternative 1
pipenv shell

# activate the environment alternative 2
pipenv run <command>

Note: consecutive steps presume the pipenv environment is being used/activated



  • Show params in help / How to pass namedtuple's signature programmatically to the Cli functions?
    • Need to do code generation i.e. write the signature into a separate python file and eval that?
    • Any fire-specific tricks to use for this? Cli(C) definition doesn't work..
      • Maybe overwriting the 'usage' portion or generating a docstring
    • Create a companion class which describes the namedtuple fields' functions
    • hardcoded defaults mechanism
  • config parser
  • decorator or some other wrapper for the cli-class to configure with given parameters without boilerplate
  • c++ template like behaviour in which you can define the named tuple with the cli class
    • code completion should work in the IDE (DONE: a hack around this..)
    • configure should know to chain config file with params
  • Configuration file requires copying fissle in the same directory with the user code
    • location independent now
  • parsing configuration and help/description require separate steps
    • would be nice to have a single point of access and import requirement
  • base level help (<script> -- -h) doesn't printout the subcommands
    • fixed in fire v0.2.1
  • look into autocompletion options (iirc, fire might have sth out-of-the-box)
    • documented


  • generate man page in a reasonable fashion
    • though fire v0.2.1 help looks like a man page
  • maybe a logging setup (--dryrun)
    • default debug logging wrapper that would log every function called
  • tooling and installation helpers
    • flit is not working on windows at least.. (works with git bash)
    • dephell or alternative to allow dev with whatever setup
  • fix doc string and args/parameter help for fire v0.2.1
  • better name
  • some sane tests
  • clean code from __init__

Project details

Download files

Download the file for your platform. If you're not sure which to choose, learn more about installing packages.

Source Distribution

fissle-0.0.4.tar.gz (10.8 kB view hashes)

Uploaded source

Built Distribution

fissle-0.0.4-py3-none-any.whl (13.4 kB view hashes)

Uploaded py3

Supported by

AWS AWS Cloud computing Datadog Datadog Monitoring Facebook / Instagram Facebook / Instagram PSF Sponsor Fastly Fastly CDN Google Google Object Storage and Download Analytics Huawei Huawei PSF Sponsor Microsoft Microsoft PSF Sponsor NVIDIA NVIDIA PSF Sponsor Pingdom Pingdom Monitoring Salesforce Salesforce PSF Sponsor Sentry Sentry Error logging StatusPage StatusPage Status page