action_hero
is a python package that helps you
manage user arguments in command line applications using argparse
Introduction
-
argparse
-
argparse
is a python standard library module used to make command line applications.argparse
providesArgumentParser
that parses user arguments and runsargparse.Action
s on them. :anchor:︎ -
action_hero
:fire: -
action_hero
makesargparse
more capable by providing a large number of custom actions. For example, theFileIsWritableAction
automatically verifies that file path(s) accepted as arguments are writable, informing the user if they aren't. This saves you the trouble of doing that check yourself. Nice, no?for many such actions.
Quick Usage
1. Installation:
pip install action_hero
2. Quick Usage: Import an action and specify it when adding an argument to your parser.
from action_hero import FileIsReadableAction ... parser.add_argument("--file", action=FileIsReadableAction) ...
3. Full Example: CLI program that counts number of lines of a file.
# examples/line_counter.py import argparse from action_hero import FileIsReadableAction if __name__ == "__main__": # Create parser parser = argparse.ArgumentParser() # Add user argument "--file" and assert that it will be readable parser.add_argument("--file", action=FileIsReadableAction) # Parse user arguments args = parser.parse_args() if args.file: # Print number of lines in file with open(args.file) as f: print("{} has {} lines".format(args.file, len(f.readlines()))) else: # Print usage if no arguments were given parser.print_usage()
Run line_counter.py
on the command line
$ ls line_counter.py mary.md $ python line_counter.py --file mary.md mary.md has 39 lines $ python line_counter.py usage: line_counter.py [-h] [--file FILE] $ python line_counter.py --file nofile.md usage: line_counter.py [-h] [--file FILE] line_counter.py: error: argument --file: File is not readable
Note: Supported Python Versions >= 3.5
Help and FAQ
Accepting action_values
There are times your action requires an additional value. For instance, when your argument accepts only filenames with md
or markdown
extensions. You can use the FileHasExtension
action for this and pass in the extensions to check for via action_values
, like so —
parser.add_argument( "--file", action=FileHasExtension, action_values=["md", "markdown"] )
Unless otherwise mentioned, action_values
should be provided as a non-empty list of strings. e.g. action_values = ["md", "markdown"]
.
Pipelining multiple actions
The PipelineAction
allows you to run multiple actions as a pipeline. Pass in your pipeline of actions as a list to action_values
. If one of the actions you're passing in has it's own action_values
, put that one as a tuple, like such: (FileHasExtension, ["md", "markdown"])
. Here's an example of pipelining actions for --file
- File has extensions
md
ormarkdown
- File exists
parser.add_argument( "--file", action=PipelineAction, action_values=[ (FileHasExtension, ["md", "markdown"]), FileExistsAction ] )
Another helpful feature, this action provides is the order of error reporting . In the above example, if the supplied argument file did not have the markdown extensions, the error message would reflect that and exit. After the user redoes the entry with a valid filename the next action in the pipeline applies FileExistsAction
which checks for existence. If the file does not exist, an error message about file not existing will be shown and exits allowing the user to try again.
This behavior can save you a lot of manual condition checks later on. For example, here's how to check for an existing, writable, non-empty , markdown file —
parser.add_argument( "--file", action=PipelineAction, action_values=[ FileExistsAction, FileIsWritableAction, FileIsNotEmptyAction, (FileHasExtension, ["md", "markdown"]) ]
Exceptions in this module
You'll come across two different exceptions in action_hero
.
-
ValueError
: These are intended for you, the CLI developer. You'd want to fix any underlying issue that causes them before releasing your CLI. e.g. whenaction_values
is an empty list. -
argparse.ArgumentError
: These are intended for your CLI's users, so they might use the messages as hints to provide corrent command line options.
Not capturing user argument exceptions
argparse.ArgumentParser
has a slightly unconventional approach to handling argparse.ArgumentError
s. Upon encountering one, it prints argument usage information, error and exits. I mention this, so you don't setup a try/except
around parser.parse_args()
to capture that exception.
In order to maintain consistency with the rest of your argparse
code, exceptions in action_hero
are also of type argparse.ArgumentError
and causes system exit as well. More information can be found in PEP 389 . Since this is expected behavior, I recommend you allow this exception and let it display usage information and exit.
Arguments accepting multiple values
Just like any other argparse.Action
each action_hero.Action
handles multiple values and provides relevant error messages.
FAQ
-
What do I need to know to use
action_hero
in my command line application? -
Vanilla
argparse
knowledge should do it. -
Where can I find information about
argparse
? -
argparse
is part of the Python standard library . -
Is
action_hero
tied to theargparse
module? -
Yes
(but technically no — any project that can use an
argpoarse.Action
should work as long as it handles theargparse.ArgumentError
exception) - What type are the user argument exceptions?
-
argparse.ArgumentError{"helpful error message"}
, just like any otherargparse.Action
- Why re-implement actions already provided by `argparse` like the `choices` action?
- In order to include them in `PipelineAction`.
- There was no mention of humans! Does this work for humans?
- Yes, it works for humans :)
Catalog
- Special actions:
Action | Description | action_values |
---|---|---|
PipelineAction |
Run multiple actions as a pipeline | Actions to run as a pipeline. e.g. [FileExistsAction, FileIsWritableAction] . () |
DebugAction |
Print debug information. There can be multiple of these in a pipeline |
- Path, Directory and File related actions:
Action | Description | action_values |
---|---|---|
DirectoryDoesNotExistAction |
Check if directory does not exist | |
DirectoryExistsAction |
Check if directory exists | |
DirectoryIsExecutableAction |
Check if directory is executable | |
DirectoryIsNotExecutableAction |
Check if directory is not executable | |
DirectoryIsNotReadableAction |
Check if directory is not readable | |
DirectoryIsNotWritableAction |
Check if directory is not writable | |
DirectoryIsReadableAction |
Check if directory is readable | |
DirectoryIsValidAction |
Check directory is valid | |
DirectoryIsWritableAction |
Check if directory is writable | |
EnsureDirectoryAction * |
Ensure directory exists and create it if it doesnt | |
EnsureFileAction * |
Ensure file exists and create it if it doesnt | |
FileDoesNotExistAction |
Check if file doesnt exist | |
FileExistsAction |
Check if file exists | |
FileIsEmptyAction |
Check if file is empty | |
FileIsExecutableAction |
Check if file is executable | |
FileIsNotEmptyAction |
Check if file is not empty | |
FileIsNotExecutableAction |
Check if file is not executable | |
FileIsNotReadableAction |
Check if file is not readable | |
FileIsNotWritableAction |
Check if file is not writable | |
FileIsReadableAction |
Check if file is readable | |
FileIsValidAction |
Check file is valid | |
FileIsWritableAction |
Check if file is writable | |
FileHasExtension |
Check if file has specified extension | Extensions to check against. e.g. ["md", "markdown"] |
PathDoesNotExistsAction |
Check if path does not exist | |
PathExistsAction |
Check if path exists | |
PathIsExecutableAction |
Check if path is executable | |
PathIsNotExecutableAction |
Check if path is not executable | |
PathIsNotReadableAction |
Check if path is not writable | |
PathIsNotWritableAction |
Check if path is not writable | |
PathIsReadableAction |
Check if path is readable | |
PathIsValidAction |
Check if path is valid | |
PathIsWritableAction |
Check if path is writable | |
ResolvePathAction † |
Resolves path to canonical path removing symbolic links if present |
- Net & Email related actions:
Action | Description | action_values |
---|---|---|
IPIsValidIPAddressAction |
Check if ip is valid ipv4 or ipv6 address | |
IPIsValidIPv4AddressAction |
Check if ip address is valid ipv4 address | |
IPIsValidIPv6AddressAction |
Check if ip address is valid ipv6 address | |
URLIsNotReachableAction |
Check if URL is not reachable | |
URLIsReachableAction |
Check if URL is reachable | |
URLWithHTTPResponseStatusCodeAction |
Check if upplied URL responds with expected HTTP response status code | Status codes to check against. e.g. ["200", "201", "202", "204"] |
EmailIsValidAction |
Checks if email address is valid |
- Type related actions:
Action | Description | action_values |
---|---|---|
IsConvertibleToFloatAction |
Check if value is convertible to float | |
IsConvertibleToIntAction |
Check if value is convertible to int | |
IsConvertibleToUUIDAction |
Checks if value is convertible to UUID | |
IsFalsyAction |
Checks if value is falsy | |
IsTruthyAction |
Checks if value is truthy |
- Range related actions:
Action | Description | action_values |
---|
- Miscellaneous actions:
Action | Description | action_values |
---|---|---|
ChoicesAction |
Argument can only have values from provided choice(s) | Choices e.g. ["red", "blue", "green"] |
NotifyAndContinueAction |
Print provided notification message(s) | Message(s) e.g. ["This command will be deprecated in the next version."] |
NotifyAndExitAction |
Print provided notification message(s) and Exit | Message(s) e.g. ["This command has been deprecated", "Try --new-command"] |
ConfirmAction |
Print provided message and proceed with user confirmation yes or no . | Message(s) e.g. ["Proceed to Installation? (Y/n)"] |
GetInputAction † |
Get user input and save to self.dest |
Message(s) e.g. ["Favorite color"] |
GetSecretInputAction † |
Get user input without displaying characters and save to the self.dest |
Message(s) e.g. ["Enter your Password"] |
LoadJSONFromFileAction † |
Return loaded JSON file(s) | |
LoadYAMLFromFileAction † |
Return loaded YAML file(s) | |
LoadPickleFromFileAction † |
Return unpickled file(s) | |
CollectIntoDictAction † |
Collect values into a dict | Delimiter(s) to split value(s) into key:value pair(s) e.g. [":", "="] (If multiple delimiters exist inside a value, only the first match is used) |
CollectIntoListAction † |
Collect values into a list | |
CollectIntoTupleAction † |
Collect values into a tuple |
* Actions that can make changes to disk
† Actions that can make changes to self.dest
Development
Notes
- Formatting -: PEP8 only. Please format with black using
black_linelength=79
- License : The MIT License
- Image Attributions : Karate by Alex Auda Samora from the Noun Project
Thank you for using action_hero
— @kadimisetty
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