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Parse positional and keyword arguments from command line
"""Parse positional and keyword arguments from `sys.argv`.
We all like :class:`argparser.ArgumentParser`. It is a great tool to build
command-line interfaces with many nice features and automatic coercing.
But sometimes it's just too verbose. At times all we need is to pass arguments
to a function from CLI. And I will help you.
Consider this ``square.py`` program::
def main(x, exp=2):
print x ** exp
Now I'd like to pass *x* to :func:`main` as command-line argument. Let's modify
our program a bit::
from simple_argparse import run_with_args
def main(x, exp=2):
print x ** exp
if __name__ == '__main__':
run_with_args(main)
Okay, I can no longer hesitate to find out what square of 11 is::
$ python square.py 11
121
Majestic! And also we can pass keyword arguments::
$ python square.py 11 3
1331
$ python square.py 11 --exp=3
1331
Note that keyword arguments without ``={value}`` part are assumed as keywords
with ``True`` value.
By the way, we can also get usage information::
$ python square.py --help
usage: square.py [--help] x [exp=2]
Under the covers arguments go through :func:`ast.literal_eval` so they will be
coerced to built-in types.
"""
import sys
from ast import literal_eval
def run_with_args(func, args=None):
"""Parse arguments from ``sys.argv`` or given list of *args* and pass
them to *func*.
If ``--help`` is passed to program, print usage information.
"""
args, kwargs = parse_args(args)
if kwargs.get('help'):
from inspect import getargspec
argspec = getargspec(func)
if argspec.defaults:
defaults_count = len(argspec.defaults)
args = argspec.args[:-defaults_count]
defaults = zip(argspec.args[-defaults_count:], argspec.defaults)
else:
args = argspec.args
defaults = []
usage = 'usage: %s [--help]' % sys.argv[0]
if args:
usage += ' ' + ' '.join(args)
if defaults:
usage += ' ' + ' '.join(('[%s=%r]' % pair for pair in defaults))
if argspec.varargs:
usage += ' ' + '*' + argspec.varargs
if argspec.keywords:
usage += ' ' + '**' + argspec.keywords
print usage
else:
return func(*args, **kwargs)
def parse_args(args=None):
"""Parse positional and keyword arguments from ``sys.argv`` or given list
of *args*.
:param args: list of string to parse, defaults to ``sys.argv[1:]``.
:return: :class:`tuple` of positional args and :class:`dict` of keyword
arguments.
Positional arguments have no specific syntax. Keyword arguments must be
written as ``--{keyword-name}={value}``::
>>> parse_args(['1', 'hello', 'True', '3.1415926', '--force=True'])
((1, 'hello', True, 3.1415926), {'force': True})
"""
if args is None:
args = sys.argv[1:]
positional_args, kwargs = (), {}
for arg in args:
if arg.startswith('--'):
arg = arg[2:]
try:
key, raw_value = arg.split('=', 1)
value = parse_literal(raw_value)
except ValueError:
key = arg
value = True
kwargs[key.replace('-', '_')] = value
else:
positional_args += (parse_literal(arg),)
return positional_args, kwargs
def parse_literal(string):
"""Parse Python literal or return *string* in case :func:`ast.literal_eval`
fails."""
try:
return literal_eval(string)
except (ValueError, SyntaxError):
return string
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