问题
I am using argparse for a python script I am writing. The purpose of the script is to process a large ascii file storing tabular data. The script just provides a convenient front-end for a class I have written that allows an arbitrary number of on-the-fly cuts to be made on the tabular data. In the class, the user can pass in a variable-name keyword argument with a two-element tuple bound to the variable. The tuple defines a lower and upper bound on whatever column with a name that corresponds to the variable-name keyword. For example:
reader = AsciiFileReducer(fname, mass = (100, float("inf")), spin = (0.5, 1))
This reader instance will then ignore all rows of the input fname except those with mass > 100 and 0.5 < spin < 1. The input fname likely has many other columns, but only mass and spin will have cuts placed on them.
I want the script I am writing to preserve this feature, but I do not know how to allow for arguments with variable names to be added with argparse.add_argument. My class allows for an arbitrary number of optional arguments, each with unspecified names where the string chosen for the name is itself meaningful. The **kwargs feature of python makes this possible. Is this possible with argparse?
回答1:
The question of accepting arbitrary key:value pairs via argparse has come up before. For example:
Using argparse with function that takes **kwargs argument
This has a couple of long answers with links to earlier questions.
Another option is to take a string and parse it with JSON.
But here's a quick choice building on nargs, and the append action type:
parser=argparse.ArgumentParser()
parser.add_argument('-k','--kwarg',nargs=3,action='append')
A sample input, produces a namespace with list of lists:
args=parser.parse_args('-k mass 100 inf -k spin 0.5 1.0'.split())
Namespace(kwarg=[['mass', '100', 'inf'], ['spin', '0.5', '1.0']])
they could be converted to a dictionary with an expression like:
vargs={key:(float(v0),float(v1)) for key,v0,v1 in args.kwarg}
which could be passed to your function as:
foo(**vargs)
{'spin': (0.5, 1.0), 'mass': (100.0, inf)}
回答2:
Apologies in advance if I didn't understand exactly what you want to do. But from your description, if I were implementing this, I might try something like the following. Here I make mass and spin optional inputs and set their default values, so the only required input is the file name.
Example code:
# q.py test code
import argparse
parser = argparse.ArgumentParser(prog='q.py')
parser.add_argument('file', help='filename')
parser.add_argument('-m', default=100, type=int, help='integer mass value')
parser.add_argument('-s', nargs=2, default=[0.5,1.0], type=float, help='spin values without comma')
args=parser.parse_args()
print('file:', args.file)
print('mass:', args.m)
print('spin:', tuple(args.s))
Some command line calls:
$ python q.py -h
usage: q.py [-h] [-m M] [-s S S] file
positional arguments:
file filename
optional arguments:
-h, --help show this help message and exit
-m M integer mass value
-s S S spin values without comma
$ python q.py test.csv
file: test.csv
mass: 100
spin: (0.5, 1.0)
$ python q.py test.csv -m 99 -s 0.2 1.1
file: test.csv
mass: 99
spin: (0.2, 1.1)
And I think you can call initialize your reader like this:
reader = AsciiFileReducer(args.file, mass = (args.m, float("inf")), spin = tuple(args.s))
来源：https://stackoverflow.com/questions/34384865/using-a-variable-keyword-for-an-optional-argument-name-with-python-argparse