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问题:
I'm using argparse to take input and pass it to a function that takes as arguments two variables and **kwargs.
Here's my function:
import requests import sys import argparse def location_by_coordinate(LAT, LNG, **kwargs): if not kwargs: coordinate_url = "https://api.instagram.com/v1/locations/search?lat=%s&lng=%s&access_token=%s" % (LAT, LNG, current_token) r = requests.get(coordinate_url).text else: coordinate_url = "https://api.instagram.com/v1/locations/search?lat=%s&lng=%s&access_token=%s" % (LAT, LNG, current_token) for key, value in kwargs.iteritems(): if 'DISTANCE' in kwargs: distance = kwargs.get('DISTANCE') if distance > 5000: print distance print "max distance is 5000m, value is reassigned to default of 1000m" distance = 1000 coordinate_url = "https://api.instagram.com/v1/locations/search?lat=%s&lng=%s&access_token=%s" % (LAT, LNG, current_token) r = requests.get(coordinate_url).text else: pass coordinate_url = "https://api.instagram.com/v1/locations/search?lat=%s&lng=%s&access_token=%s" % (LAT, LNG, current_token) r = requests.get(coordinate_url).text if 'FACEBOOK_PLACES_ID' in kwargs: fb_places_id = kwargs.get('FACEBOOK_PLACES_ID') payload = {'FACEBOOK_PLACES_ID': '%s' % (fb_places_id), 'DISTANCE': '%s' % (DISTANCE)} r = requests.get(coordinate_url, params=payload).text if 'FOURSQUARE_ID' in kwargs: foursquare_id = kwargs.get('FOURSQUARE_ID') payload = {'FOURSQUARE_ID': '%s' % (foursquare_id), 'DISTANCE': '%s' % (DISTANCE)} r = requests.get(coordinate_url, params=payload).text if 'FOURSQUARE_V2_ID' in kwargs: foursquare_v2_id = kwargs.get('FOURSQUARE_V2_ID') payload = {'FOURSQUARE_V2_ID': '%s' % (foursquare_v2_id), 'DISTANCE': '%s' % (DISTANCE)} r = requests.get(coordinate_url, params=payload).text #print r return r
Given this function and its use of **kwargs, how should I setup the subparsers?
Here's how I've setup the command line parser thus far:
def main(): parser = argparse.ArgumentParser(description="API Endpoints tester") subparsers = parser.add_subparsers(dest="command", help="Available commands") location_by_parser = subparsers.add_parser("location_by_coordinate", help="location function") location_by_parser.add_argument("LAT", help="latitude") location_by_parser.add_argument("LNG", help="longitude") arguments = parser.parse_args(sys.argv[1:]) arguments = vars(arguments) command = arguments.pop("command") if command == "location_by_coordinate": LAT, LNG = location_by_coordinate(**arguments) else: print "No command provided..." if __name__ == "__main__": main()
Obviously, the above main() function works fine with the location_by_coordinate() function when I call it at the command line like this:
$ python argstest.py location_by_coordinate 40.5949799 -73.9495148
But with the code the way it is currently, if I try:
$ python argstest.py location_by_coordinate 40.5949799 -73.9495148 DISTANCE=3000
Obviously, I get:
argstest.py: error: unrecognized arguments: DISTANCE=3000
But I'm not sure how to setup a subparser for **kwargs. If I try to setup a subparser like this:
location_by_parser.add_argument("**kwargs", help="**kwargs")
and then try that command again:
$ python argstest.py location_by_coordinate 40.5949799 -73.9495148 DISTANCE=3000
That doesn't work because the arguments object (which is a dictionary), becomes this:
{'LAT': '40.5949799', 'LNG': '-73.9495148', 'command': 'location_by_coordinate', '**kwargs': 'DISTANCE=3000'}
And this Traceback is returned:
Traceback (most recent call last): File "argstest.py", line 118, in <module> main() File "argstest.py", line 108, in main foo = location_by_coordinate(**arguments) File "argstest.py", line 40, in location_by_coordinate return r UnboundLocalError: local variable 'r' referenced before assignment
How can I enable argparse to handle/to parse what is entered at the command line that is intended to be passed to the function via **kwargs?
回答1:
Do you understand what is going on with the
{'LAT': '40.5949799', 'LNG': '-73.9495148', 'command': 'location_by_coordinate', '**kwargs': 'DISTANCE=3000'}
arguments dictionary? You defined a 'positional' argument with the name ('dest') of '**kwargs'. You could just as well named it 'foobar'. The parser assigned the string 'DISTANCE=3000' to that attribute in the args namespace, which turned into a dictionary key:value pair in arguments.
You could, of course, look for arguments['**kwargs'], and parse the value for yourself:
v = arguments['**kwargs'] # or pop if you prefer if v is not None: k, v = v.split('=') arguments[k] = int(v)
It could be generalized to handle multiple pairs (defined with `nargs='*').
argparse does not handle arguments the same way as Python functions, so there's nothing exactly analogous the **kwargs.
The normal way to accept something like distance is with 'optionals' or flagged arguments.
parser.add_argument('-d','--distance', type=int, help=...)
which will accept
python argstest.py location_by_coordinate 40.5949799 -73.9495148 --distance=3000 python argstest.py location_by_coordinate 40.5949799 -73.9495148 --distance 3000 python argstest.py location_by_coordinate 40.5949799 -73.9495148 --d3000 python argstest.py location_by_coordinate 40.5949799 -73.9495148
It could also be setup to use --DISTANCE or other names. In the last case args namespace will have a default value for distance. The default default is None.
That's the straight forward way of adding kwarg like arguments to argparse.
Accepting arbitrary dictionary like pairs, distance:3000, distance=3000, has been asked before on SO. The answers have always been some variation of the parsing that I sketched above. It could be done in a custom Action class, or post parsing as I suggest.
oops, this answer is nearly a clone of one I wrote a few days ago: https://stackoverflow.com/a/33639147/901925
A similar 2011 question: Using argparse to parse arguments of form "arg= val"
Python argparse dict arg
=================================
(edit)
Example with a function that takes *args:
In [2]: import argparse In [3]: def foo(*args, **kwargs): ...: print('args',args) ...: print('kwargs',kwargs) ...: In [4]: parser=argparse.ArgumentParser() In [5]: parser.add_argument('arg1') In [6]: parser.add_argument('arg2',nargs='+') In [7]: args=parser.parse_args('one two three'.split()) In [8]: args Out[8]: Namespace(arg1='one', arg2=['two', 'three'])
So I have 2 positional arguments, one with a single string value, the other with a list (due to the + nargs).
Call foo with these args attributes:
In [10]: foo(args.arg1) args ('one',) kwargs {} In [11]: foo(args.arg1, args.arg2) args ('one', ['two', 'three']) kwargs {} In [12]: foo(args.arg1, arg2=args.arg2) args ('one',) kwargs {'arg2': ['two', 'three']}
I defined 'positionals', but it would have worked just as well with 'optionals'. The distinction between positionals and optionals disappears in the namespace.
If I convert the namespace to a dictionary, I can pass values to foo in various ways, either through the *args or through **kwargs. It's all in how I call foo, not in how they appear in args or arguments. None of this is unique to argparse.
In [13]: arguments = vars(args) In [14]: arguments Out[14]: {'arg2': ['two', 'three'], 'arg1': 'one'} In [15]: foo(arguments['arg2'], arguments['arg1']) args (['two', 'three'], 'one') kwargs {} In [16]: foo(arguments['arg2'], arguments) args (['two', 'three'], {'arg2': ['two', 'three'], 'arg1': 'one'}) kwargs {} In [17]: foo(arguments['arg2'], **arguments) args (['two', 'three'],) kwargs {'arg2': ['two', 'three'], 'arg1': 'one'} In [24]: foo(*arguments, **arguments) args ('arg2', 'arg1') # *args is the keys of arguments kwargs {'arg2': ['two', 'three'], 'arg1': 'one'} In [25]: foo(*arguments.values(), **arguments) args (['two', 'three'], 'one') # *args is the values of arguments kwargs {'arg2': ['two', 'three'], 'arg1': 'one'}
回答2:
How can I enable argparse to handle/to parse what is entered at the command line that is intended to be passed to the function via **kwargs?
This command:
$ python argstest.py location_by_coordinate 40.5949799 -73.9495148 DISTANCE=3000
does NOT execute the function call:
location_by_coordinate(40.5949799, -73.9495148, DISTANCE=3000)
That is easy to prove:
def location_by_coordinate(x, y, **kwargs): print "I was called!"
Go ahead and parse the args, and you'll see that the function isn't called. As a result, all your work setting up a subparser with the name location_by_coordinate was in vain.
The argparse module just examines sys.argv, which is a simple list of strings. Each string is one of the 'words' entered on the command line after the python command.
By default, the argument strings are taken from sys.argv,...
https://docs.python.org/3/library/argparse.html#the-parse-args-method
Yeah, sys.argv is a scary name, but a list of strings is just a list of strings. If you look at the argparse docs, all the examples do this:
parser.parse_args('--foo FOO'.split())
A list of strings you create with split() is no different than some list of strings that sys.argv refers to.
You need to call your location_by_coordinate() function yourself. In order to do that, you need to get the args from the command line, assemble the args that should be kwargs in a dictionary, and call your function like this:
location_by_coordinate(lat, lon, **my_dict)
If you have these values:
lat = 10 lon = 20 my_dict = {'a': 1, 'b': 2}
then the function call above will be equivalent to:
location_by_coordinate(10, 20, a=1, b=2)
Here is an example:
import argparse def dostuff(x, y, **kwargs): print x, y, kwargs parser = argparse.ArgumentParser() parser.add_argument("LAT") parser.add_argument("LON") parser.add_argument("--distance") args = parser.parse_args() my_dict = {} my_dict["distance"] = args.distance dostuff(args.LAT, args.LON, **my_dict) $ python my_prog.py 10 20 --distance 1 10 20 {'distance': '1'}
You can also get a dict from the parser:
... ... args = parser.parse_args() args_dict = vars(args) print args_dict --output:-- {'LAT': '10', 'distance': '1', 'LON': '20'} lat = args_dict.pop('LAT') lon = args_dict.pop('LON') print args_dict --output:-- {'distance': '1'} location_by_coordinates(lat, lon, **args_dict)
If you want to make the user type:
DISTANCE=3000
on the command line, first of all I would not make them type all caps, so lets make the goal:
distance=3000
Add another mandatory argument to the parser:
location_by_parser.add_argument("distance", help="distance")
Then after you parse the following:
$ python argstest.py location_by_coordinate 40.5949799 -73.9495148 distance=3000
you can do this:
arguments = parser.parse_args() args_dict = vars(arguments)
The args_dict will contain the key/value pair 'distance': 'distance=3000'. You can change that dict entry to 'distance': '3000' by doing the following:
pieces = args_dict['distance'].split('=') if len(pieces) == 2 and pieces[0] == 'distance': args_dict['distance'] = pieces[1]
Or, you can set things up so that the parser will automatically execute that code by creating a custom action that executes when the distance arg is parsed:
class DistanceAction(argparse.Action): def __call__(self, parser, namespace, values, option_string=None): #values => The value for the distance command line arg pieces = values.split('=') if len(pieces) == 2 and pieces[0] in ['distance', 'wave_action']: #only allow 'distance=' and 'wave_action=' setattr(namespace, self.dest, pieces[1]) #The dest key specified in the parser gets assigned the value else: raise argparse.ArgumentTypeError('Usage: distance=3000. Only distance=, wave_action= allowed.')
You can use the action like this:
location_by_parser.add_argument( "distance", help="longitude", action=DistanceAction )
And if you want to get fancy, you can collect all the name=val args specified on the command line into one dictionary named, say, keyword_args, which will allow you to call your method like this:
args = parser.parse_args() args_dict = vars(args) keyword_args = args_dict["keyword_args"] location_by_coordinates(lat, lon, **keyword_args)
Here's the parser configuration:
location_by_parser.add_argument( "keyword_args", help="extra args", nargs='*', action=DistanceAction )
import argparse import sys def location_by_coordinates(x, y, **kwargs): print x print y print kwargs class DistanceAction(argparse.Action): def __call__(self, parser, namespace, values, option_string=None): allowed_keywords = ['distance', 'wave_action'] keyword_dict = {} for arg in values: #values => The args found for keyword_args pieces = arg.split('=') if len(pieces) == 2 and pieces[0] in allowed_keywords: keyword_dict[pieces[0]] = pieces[1] else: #raise an error #Create error message: msg_inserts = ['{}='] * len(allowed_keywords) msg_template = 'Example usage: distance=3000. Only {} allowed.'.format(', '.join(msg_inserts)) msg = msg_template.format(*allowed_keywords) raise argparse.ArgumentTypeError(msg) setattr(namespace, self.dest, keyword_dict) #The dest key specified in the #parser gets assigned the keyword_dict--in #this case it defaults to 'keyword_args' parser = argparse.ArgumentParser(description="API Endpoints tester") subparsers = parser.add_subparsers(dest="command", help="Available commands") location_by_parser = subparsers.add_parser("location_by_coordinate", help="location function") location_by_parser.add_argument("LAT", help="latitude") location_by_parser.add_argument("LNG", help="longitude") location_by_parser.add_argument("keyword_args", help="extra args", nargs='*', action=DistanceAction) arguments = parser.parse_args() args_dict = vars(arguments) print args_dict lat = args_dict['LAT'] lon = args_dict['LNG'] keyword_args = args_dict['keyword_args'] location_by_coordinates(lat, lon, **keyword_args)
Example:
$ python prog.py location_by_coordinate 40.5949799 -73.9495148 distance=3000 wave_action=1.4 {'LAT': '40.5949799', 'LNG': '-73.9495148', 'command': 'location_by_coordinate', 'keyword_args': {'distance': '3000', 'wave_action': '1.4'}} 40.5949799 -73.9495148 {'distance': '3000', 'wave_action': '1.4'} $ python prog.py location_by_coordinate 40.5949799 -73.9495148 x=10 ... ... File "2.py", line 25, in __call__ raise argparse.ArgumentTypeError(msg) argparse.ArgumentTypeError: Example usage: distance=3000. Only distance=, wave_action= allowed.
