Usage

Declaring flags

Declare flags with the global parser instance:

import arglite

arglite.parser.require("name", type=str)
arglite.parser.optional("count", default=1, type=int)
arglite.parser.flag("verbose")

Method	Purpose
parser.require(name, type=None)	Required flag. Exits with an error if missing.
parser.optional(name, default=None, type=None)	Optional flag with a default value.
parser.flag(name)	Boolean flag. True if present, otherwise False.

Accessing values

Access declared flags as attributes on the parser. The first time you access a flag, arglite parses sys.argv.

print(arglite.parser.name)
print(arglite.parser.count)
print(arglite.parser.verbose)

Short flags

If you do not provide a short alias, the first letter of the flag name is used automatically.

arglite.parser.require("name")

All of these work:

python demo.py --name Yo
python demo.py -n Yo
python demo.py --name=Yo
python demo.py -n=Yo

You can also set an explicit short alias:

arglite.parser.require("name", short="x")

Types

arglite converts values automatically.

arglite.parser.require("count", type=int)
arglite.parser.require("ratio", type=float)
arglite.parser.optional("debug", default=False, type=bool)

Boolean flags are the easiest way to get a simple on/off switch:

arglite.parser.flag("verbose")

• --verbose → True
• absent → False
• --verbose=false → False

Edge cases

Values with spaces

Use normal shell quoting:

python demo.py --message "hello world"

Empty strings

Empty strings are preserved:

python demo.py --name ""

Negative numbers

Values that start with - are handled correctly when they follow a value-expecting flag:

python demo.py --offset -5

Errors

arglite exits with code 1 and a clear message when something is wrong:

✗ ERROR: --name is required but was not provided
✗ ERROR: Unknown flag --foo; the program does not call for it
✗ ERROR: Value for --count could not be converted to int: 'abc'