I'm trying to write a script that accepts multiple input sources and does something to each one. Something like this
./my_script.py \
-i input1_url input1_name input1_other_var \
-i input2_url input2_name input2_other_var \
-i input3_url input3_name
# notice inputX_other_var is optional
But I can't quite figure out how to do this using argparse. It seems that it's set up so that each option flag can only be used once. I know how to associate multiple arguments with a single option (nargs='*' or nargs='+'), but that still won't let me use the -i flag multiple times. How do I go about accomplishing this?
Just to be clear, what I would like in the end is a list of lists of strings. So
[["input1_url", "input1_name", "input1_other"],
["input2_url", "input2_name", "input2_other"],
["input3_url", "input3_name"]]
Here's a parser that handles a repeated 2 argument optional - with names defined in the metavar:
parser=argparse.ArgumentParser()
parser.add_argument('-i','--input',action='append',nargs=2,
metavar=('url','name'),help='help:')
In [295]: parser.print_help()
usage: ipython2.7 [-h] [-i url name]
optional arguments:
-h, --help show this help message and exit
-i url name, --input url name
help:
In [296]: parser.parse_args('-i one two -i three four'.split())
Out[296]: Namespace(input=[['one', 'two'], ['three', 'four']])
This does not handle the 2 or 3 argument case (though I wrote a patch some time ago for a Python bug/issue that would handle such a range).
How about a separate argument definition with nargs=3 and metavar=('url','name','other')?
The tuple metavar can also be used with nargs='+' and nargs='*'; the 2 strings are used as [-u A [B ...]] or [-u [A [B ...]]].
This is simple; just add both action='append' and nargs='*' (or '+').
import argparse
parser = argparse.ArgumentParser()
parser.add_argument('-i', action='append', nargs='+')
args = parser.parse_args()
Then when you run it, you get
In [32]: run test.py -i input1_url input1_name input1_other_var -i input2_url i
...: nput2_name input2_other_var -i input3_url input3_name
In [33]: args.i
Out[33]:
[['input1_url', 'input1_name', 'input1_other_var'],
['input2_url', 'input2_name', 'input2_other_var'],
['input3_url', 'input3_name']]
-i should be configured to accept 3 arguments and to use the append action.
>>> p = argparse.ArgumentParser()
>>> p.add_argument("-i", nargs=3, action='append')
_AppendAction(...)
>>> p.parse_args("-i a b c -i d e f -i g h i".split())
Namespace(i=[['a', 'b', 'c'], ['d', 'e', 'f'], ['g', 'h', 'i']])
To handle an optional value, you might try using a simple custom type. In this case, the argument to -i is a single comma-delimited string, with the number of splits limited to 2. You would need to post-process the values to ensure there are at least two values specified.
>>> p.add_argument("-i", type=lambda x: x.split(",", 2), action='append')
>>> print p.parse_args("-i a,b,c -i d,e -i g,h,i,j".split())
Namespace(i=[['a', 'b', 'c'], ['d', 'e'], ['g', 'h', 'i,j']])
For more control, define a custom action. This one extends the built-in _AppendAction (used by action='append'), but just does some range checking on the number of arguments given to -i.
class TwoOrThree(argparse._AppendAction):
def __call__(self, parser, namespace, values, option_string=None):
if not (2 <= len(values) <= 3):
raise argparse.ArgumentError(self, "%s takes 2 or 3 values, %d given" % (option_string, len(values)))
super(TwoOrThree, self).__call__(parser, namespace, values, option_string)
p.add_argument("-i", nargs='+', action=TwoOrThree)
Adding with Other in this Thread.
If you use action='append' in add_argument() then you will get arguments in list(s) within a list every time you add the option.
As you liked:
[
["input1_url", "input1_name", "input1_other"],
["input2_url", "input2_name", "input2_other"],
["input3_url", "input3_name"]
]
But if anyone wants those arguments in the same list[], then use action='extend' instead of action='append' in your code. This will give you those arguments in a single list.
[
"input1_url",
"input1_name",
"input1_other",
"input2_url",
"input2_name",
"input2_other",
"input3_url",
"input3_name"
]
Related
I have an argparse argument that appends, and I want it to be called at least twice. (args.option would contain at least two lists) I know that one way would be to check it myself, but I would prefer a way to make argparse do it.
import argparse
parser = argparse.ArgumentParser(description='Do the thing')
parser.add_argument('-o', '--option', nargs=3, action='append', metavar=('A', 'B', 'C'))
args = parser.parse_args()
...
With that argument, each time you use a '-o' flag, it looks for 3 strings, and it puts them in a list in the output:
In [127]: import argparse
...:
...: parser = argparse.ArgumentParser(description='Do the thing')
...: parser.add_argument('-o', '--option', nargs=3, action='append', metavar=('A', 'B', 'C'));
In [128]: parser.print_help()
usage: ipykernel_launcher.py [-h] [-o A B C]
Do the thing
optional arguments:
-h, --help show this help message and exit
-o A B C, --option A B C
In [129]: parser.parse_args('-o 1 2 3 -o a b c'.split())
Out[129]: Namespace(option=[['1', '2', '3'], ['a', 'b', 'c']])
There's no mechanism in argparse to check the length of args.option. Nor any meta-nargs to requires the double use of '-o'.
In [130]: parser.parse_args(''.split())
Out[130]: Namespace(option=None
In [131]: parser.parse_args('-o 1 2 3'.split())
Out[131]: Namespace(option=[['1', '2', '3']])
You could define 2 positionals with the same dest. The parsing works ok, but the usage formatting has problem, raising error with both help and error messages. I'd stick with checking len(args.option).
I would like to be able to support positional command line arguments that go into different lists based on prior predicates.
For example, a command like:
mycommand one two three
would yield args like:
main_dest = ['one','two','three']
other_dest = []
but a command like:
mycommand one --other two three --main four five
would yield args like:
main_dest = ['one','four','five']
other_dest = ['two','three']
Conceptually what I'd like is an action that modifies the dest of the positional argument reader.
As a first try this set of Actions seems to do the trick:
In [73]: parser = argparse.ArgumentParser()
In [74]: parser.add_argument('main', nargs='*');
In [75]: parser.add_argument('other', nargs='*');
In [76]: parser.add_argument('--main', action='append');
In [77]: parser.add_argument('--other', action='append');
In [78]: parser.print_usage()
usage: ipython3 [-h] [--main MAIN] [--other OTHER]
[main [main ...]] [other [other ...]]
In [79]: parser.parse_args('one two three'.split())
Out[79]: Namespace(main=['one', 'two', 'three'], other=[])
In [80]: parser.parse_args('one --other two --main three'.split())
Out[80]: Namespace(main=['one', 'three'], other=['two'])
74 and 76 both have main as their dest. I use append for the flagged ones so they don't overwrite positional values. But despite what the usage shows, positionals will only work at the start. If placed a the end they'll overwrite flagged values. And the 'other' positional will never get values - so I should have omitted it.
So it is possible to play games like this, but I'm not sure it's robust, or any easier for your users.
argparse: flatten the result of action='append'
Firstly, I apologize if my title is misleading/ unclear as I am really not sure what is the best way to put it.
I have 3 optional arguments, which uses action='store_true'. Let's keep the argument flags to -va, -vb, -vc
var_list = ['a', 'b', 'c']
if args.va:
run_this_func(var_list[0])
if args.vb:
run_this_func(var_list[1])
if args.vc:
run_this_func(var_list[2])
if not args.higha and not args.highb and not args.highmem:
for var in var_list:
run_this_func(var)
if args.va and args.vb:
run_this_func(var_list[:-1])
if args.vb and args.vc:
run_this_func(var_list[1:])
if args.vc and args.va:
run_this_func(var_list[0], var_list[2])
How can I code in more efficient way? The above method that I had utilized while it may work, seems more like a roundabout way to get things going...
Initially I am thinking of using tuple such that it will be something such as input = (args.va, args.vb, args.vc) so that it may return me eg. (True, False, False)... Not sure if that is ideal though.
Any advice?
I think you can use tuple too.
var_list = ['a', 'b', 'c']
input = (args.va, args.vb, args.vc)
vars = [item for index, item in enumerate(var_list) if args_tuple[index]]
run_this_func(*vars)
I think this is a case where argparse.add_argument's nargs and choices keywords can be used to get the list that you want (some subset of [a,b,c]) without having to filter based on multiple arguments.
I would recommend doing something like this:
parser = argparse.ArgumentParser()
parser.add_argument('-v', choices=['a','b','c'], nargs='+')
args = parser.parse_args()
This says: create an optional argument -v that can take one or multiple values but each of those values must be one of ['a','b','c']
Then you can pass it arguments from the command line like this (for example):
$ python my_file.py -v a c
which means that args will look like: Namespace(v=['a', 'c'])
and args.v looks like ['a', 'c'] which is the list you were looking for (and without any filtering!)
You can then call your function as:
run_this_func(args.v)
I am trying to build a command line parser that will be able to share between arguments the values passed in order to avoid having to type them multiple times. Said otherwise, I would like the namespaces of both argument to be identical:
import argparse
class PrintAction(argparse.Action):
def __init__(self, option_strings, dest, **kwargs):
super(PrintAction, self).__init__(option_strings, dest, **kwargs)
def __call__(self, parser, namespace, values, option_string=None):
for val in values:
print(val)
parser = argparse.ArgumentParser(description='A foo that foos and a bar that bars')
parser.add_argument('--foo', action=PrintAction)
parser.add_argument('bar', nargs='+')
args = parser.parse_args(['--foo', 'a', 'b', 'c']) # Case 1
args = parser.parse_args(['a', 'b', 'c']) # Case 2
I would then like a solution that stores in both cases ['a', 'b', 'c'] in bar but also that in the case that --foo is provided, then a, b and c would be printed.
For now, what I get is foo prints only a and bar stores only b and c in case 1 and the correct result in case 2.
You need to make --foo a boolean flag. Now it's a string parameter, because you did not state otherwise. Set action to store_true for the boolean flag effect.
The final solution would look like:
def print_args(args):
if args.foo:
for val in args.bar:
print(val)
parser = argparse.ArgumentParser(description='A foo that foos and a bar that bars')
parser.add_argument('--foo', action='store_true')
parser.add_argument('bar', nargs='+')
args = parser.parse_args(['--foo', 'a', 'b', 'c']) # Case 1
args = parser.parse_args(['a', 'b', 'c']) # Case 2
Then calling print_args(args) in the first case will print a, b and c and in the second case, it won't.
You can't (readily) trick the argparse into reusing argv strings. The parser allocates values to the Actions.
The default nargs is None, which means, use the the next string as an argument.
parser.add_argument('--foo')
would set foo='a', and bar=['b','c'].
In your Action, values will be ['a'], which you print. In optparse each option gets the remaining argv list, which it can consume as it wants. In argparse it only gets the values that its nargs demands.
You could specify in the __init__ that the nargs=0, and then print from sys.argv. Eqivalently, as #9000 suggests, make it a store_true and print after parsing. Look at the code for the store_true Action class.
Another option is to give both foo and bar a *, and have foo both print and save to the bar dest. Then foo would consume all following strings. But, if bar doesn't have anything to save, it might write [] to the namespace.
In any case, the best you can do is fake the repeated use.
Another idea is to use 2 different parsers with parse_known_args. Parsers don't mess with the sys.argv, so it can read and parsed multiple times.
As shown in the following code, I want to have an optional positional argument files, I want to specify a default value for it, when paths are passed in, use specified path.
But because --bar can have multiple arguments, the path passed in didn't go into args.files, how do I fix that? Thanks!
import argparse
parser = argparse.ArgumentParser()
parser.add_argument('--foo')
parser.add_argument('--bar', nargs='*')
parser.add_argument('files', nargs='?')
cmd = '--foo a --bar b c d '
print parser.parse_args(cmd.split())
# Namespace(bar=['b', 'c', 'd'], files=None, foo='a')
cmd = '--foo a --bar b c d /path/to/file1'
print parser.parse_args(cmd.split())
# Namespace(bar=['b', 'c', 'd', '/path/to/file1'], files=None, foo='a')
Your argument spec is inherently ambiguous (since --bar can take infinite arguments, there is no good way to tell when it ends, particularly since files is optional), so it requires user disambiguation. Specifically, argparse can be told "this is the end of the switches section, all subsequent argument are positional" by putting -- before the positional only section. If you do:
cmd = '--foo a --bar b c d -- /path/to/file1'
print parser.parse_args(cmd.split())
You should get:
Namespace(bar=['b', 'c', 'd'], files='/path/to/file1', foo='a')
(Tested on Py3, but should apply to Py2 as well)
Alternatively, the user can pass the positional argument anywhere it's unambiguous by avoiding putting positional arguments after --bar e.g.:
cmd = '/path/to/file1 --foo a --bar b c d'
or
cmd = '--foo a /path/to/file1 --bar b c d'
Lastly, you could avoid using nargs='*' for switches, given the ambiguity it introduces. Instead, define --bar to be accepted multiple times with a single value per switch, accumulating all uses to a list:
parser.add_argument('--bar', action='append')
then you pass --bar multiple times to supply multiple values one at a time, instead of passing it once with many values:
cmd = '--foo a --bar b --bar c --bar d /path/to/file1'