ApeGears

An improved ArgumentParser, fully compatible with the standard argparse.ArgumentParser.

What is ApeGears?

ApeGears' goal is making it easier to use the ArgumentParser. It provides simple and intuitive tools for achieving the most common use cases.

ApeGears defines an ArgumentParser which is a subclass of argparse.ArgumentParser, and is fully compatible with it.

What is wrong with argparse?

Nothing. It works great.

However, it seems to be putting too much emphasis on being powerful, and too little on being intuitive. For some actions, its interface is overly complicated. The most common operations (e.g. defining flags and list arguments) are sometimes not perfectly intuitive.

Furthermore, it seems to be missing some useful options, such as support for dict arguments. Also, using arguments of custom types (using the type parameter) doesn't work as smoothly as you'd hope.

Another annoyance is that when using FileType in write-mode, the output file is created very early (while parsing cli args), not giving the option in your script to decide not to write to it after all.

Feaures

Following is an overview of the main features. See below for more details on each.

• Intuitive "adder" methods for defining arguments: add_positional, add_optional, add_flag, add_list.
  • These cover the most common use cases. You'd hardly ever need to use the basic add_argument method.
• Dict arguments, using add_dict method.
• Defining custom argument-types is simpler and more powerful, using "specs".
• Builtin support for some standard python types.
  • E.g. range, date, datetime, Path, literals, IP address, regular expression.
• An alternative FileType argument type, better than argparse.FileType.
• Smooth integration with fileinput.
• Builtin support for enum arguments.
• Builtin support for overriding log levels from cli, using lo99ing.
• Can extract description from docstring of caller module, to avoid doc duplication (enable by passing: description=CALLER_DOC)
• Integration with other ArgumentParser-related tools.
  • argcomplete
  • func_argparse

Avoiding argparse bugs:

• Issue16399 append-with-nonempty-default: apegears includes an easy-to-use workaround.
• Issue13041 terminal width is not detected properly: this is fixed in python 3.8, but using apegears avoids the issue for all version.

Adder methods

The standard all-in-one add_argument method is powerful, but not intuitive for some uses. It has many kwargs, and not all combinations make sense.

Instead, in most cases, you can use the more precise and convenient adder methods:

• add_positional -- for defining positional arguments.

• add_optional -- for defining optional (i.e. non-positional) arguments.

• add_flag -- for defining (optional) flags ("switches").

• add_list -- for defining (optional) list arguments.

  • Multiple values can be passed in a single arg, or multiple. The following are equivalent, and result with {'chars': ['a', 'b', 'c', 'd']}:

    % prog.py --chars a b c d
    % prog.py --chars a b --chars c d
    % prog.py --chars a --chars b --chars c --chars d
    

You can still use the add_argument method for "advanced" argument definitions, but you'd rarely need to.

Dict arguments

Use add_dict for defining dict optional arguments. E.g.:

parser.add_dict('--overrides')
parser.parse_args('--overrides log_level=debug logfile=out.log'.split()).overrides
=> OrderedDict([('log_level', 'debug'), ('logfile', 'out.log')])

Similar to list arguments, multiple key-value pairs can be passed in a single arg, or multiple.

Custom argument types

argparse supports adding argument types by passing type=callable, where callable converts the CLI string value to whatever you want (e.g. int converts the string to an integer).

This is not powerful enough, because often, when defining how a new argument type behaves, you'd want to include more than just how to convert a CLI string.

ApeGears makes use of Argument Type Specs, which supports defining defaults for several fields:

• names
• default
• choices
• help
• metavar

Each of these can be explicitly overridden when calling the adder function.

Suppose you have a type T which you want to use with the parser, so you define a spec for it, Tspec.

For supporting usage like parser.add_xxx(..., type=T, ...), you either:

• register the spec: register_spec(T, Tspec)
• define a class attribute named __argparse__. E.g.: T.__argparse__ = Tspec

Alternatively, this also works: parser.add_xxx(..., type=Tspec, ...)

Argument types for standard python types

Argument type specs are predefined for some standard python types. E.g., range, date, datetime, path, literals, IP address, regular expression.

Can be used like this:

parser.add_optional(..., type='date', ...)  # also works: type=datetime.date
parser.parse_args('--date 2020-03-04'.split()).date
=> datetime.date(2020, 3, 4)

Another example:

parser.add_optional('indexes', ..., type='range', ...)  # also works: type=range
parser.parse_args('--indexes 0:100:10'.split()).indexes
=> range(0, 100, 10)

Another example, for using literals (inspired by python-fire):

parser.add_optional('val', ..., type='literal', ...) parser.parse_args('--val {"four":4,"six":6}'.split()).val {'four': 4, 'six': 6} # this is a dict

Improved FileType

The problem with argparse.FileType, is that in write-mode, the file is opened (created) during cli-parsing, even in cases where you wouldn't want to write to the file.

For example, if your script is using argparse and takes a positional output file (mode='w'), The following invocations will create an empty file named foo (deleting it if already exists):

% myscript.py foo -h  # will create the file, and print help message
% myscript.py foo --no-such-option  # will create the file, and print argparse error message

There are other cases where you would decide not to write to output file (e.g. you fail generating the content), but using argparse.FileType would still create an empty file (deleting existing one).

The solution is using apegears.FileType instead, which lazily opens the file, when it is first accessed.

fileinput arguments

When you want to use fileinput in your script, apegears can save you a few lines of code:

from apegears import ArgumentParser, fileinput
parser = ArgumentParser()
parser.add_positional(type=fileinput(decompress=True), nargs='*')
args = parser.parse_args()
for line in args.infiles:
    ...

Also, passing decompress=True handles compressed files better than using fileinput directly with hook_compressed (see issue5758).

Enum arguments

Enum types are also supported as argument types:

class Direction(Enum):
    UP = 1
    DOWN = 2
    LEFT = 3
    RIGHT = 4

parser.add_optional(type=Direction)
parser.parse_args('--direction LEFT'.split()).direction
=> <Direction.LEFT: 3>

Overriding log levels from cli

If you're using lo99ing, the parser automatically includes a -L/--log-level option for overriding log levels from cli.

E.g., to override from cli:

myscript.py -L mylogger.traffic=debug yourlogger=error

The append-with-nonempty-default issue

You might have encountered a bug when using list arguments in the standard ArgumentParser:

from argparse import ArgumentParser
parser = ArgumentParser()
parser.add_argument('list', action='append', default=['D'])
parser.parse_args('X'.split()).list
=> ['D', 'X']  # expected: ['X']

Basically, default, instead of being used as a default value, is used as an initial value.

There is no easy-to-use workaround in the argparser level, but ApeGears provides one.

The add_list and add_dict methods include a workaround this issue. It is enabled by default.

If you use the add_argument method directly, the workaround is disabled (for being compatible with argparse), but you can enable it by passing strict_default=True.

Integration with other ArgumentParser-related tools

argcomplete

argcomplete allows "command line tab completion of arguments for your Python script".

For argcomplete users, there are a few (minor) advantages to using ApeGears ArgumentParser, over argparse's:

• No need to call argcomplete.autocomplete(parser), it is called automatically for you
• Better completion of enum types
• Avoids the awkward way of setting a custom completer
  • use like: parser.add_argument(..., completer=MyCompleter)
  • instead of: parser.add_argument(...).completer = MyCompleter
• If you define custom argument types, you can also define a completer as part of their spec

func_argparse

func_argparse is used for "Generating a nice command line interface for a list of functions or a module".

ApeGears lets you use func_argparse for generating an ApeGears ArgumentParser, instead of argparse's.

The main advantages of using apegears + func_argparse over using func_argparse alone:

• Dict options
• Custom argument types, and argument types for standard python types

To use it, simply replace your import lines:

import func_argparse            -->    import apegears.func_argparse
from func_argparse import ...   -->    from apegears.func_argparse import ...

Getting Started

Installation

Using pip:

pip install apegears

Start using the ArgumentParser

apegears.ArgumentParser is fully compatible with argparse's, so you can start by replacing your import lines:

import argparse            -->  import apegears
from argparse import ...   -->  from apegears import ...

... to unleash the apes.

What does the Name Mean?

Nothing.

argparse = list('argparse')
apegears = list('apegears')
while argparse != apegears:
    random.shuffle(argparse)
print('Got it?')
print('Probably not...')