Can I check if the value was provided by default or by user?
Is there a way, when used, to argparse
determine if a field has a value because the user specified it or because it was not specified and got a default value? Note. I would also like to consider the case where the user explicitly specifies a default.
I would like to use argparse
to handle command line arguments, and I would like to use formatter_class=argparse.ArgumentDefaultsHelpFormatter
to display default values for fields that are not specified. Also, I would like to read the values from the config file.
If the user specifies a value on the command line, I would like to make sure that I use that value (even if that value is the default but explicitly specified). If the user hasn't provided a value, but one is found in the config file, I would like to use it. If the user has not specified it on the command line and there is no value in the config file, I would like to use the default that was specified in the statement above.
So, I can customize the parsing like
parser = parser = argparse.ArgumentParser( description="""Tool with many ways to get values""", formatter_class=argparse.ArgumentDefaultsHelpFormatter )
parser.add_argument( '-p', '--path', help="The path to a file to read", default="data.csv" )
parser.add_argument( '-c', '--conf', help="The config file to use", default="config.txt" )
and there are probably many other parameters.
Now I would like to also read the config file which can include the value
data_path = data2.csv
So, if the user specifies -p
on the command line, I would like to read this file; if they don't, and I am using this config file, I would like to read data2.csv
; and if I use a config file that doesn't define data_path
, and they don't specify -p
, I would like to use the default data.csv
.
The main tricky case for me would be if the user specifies -p data.csv
then it will have a default but should take precedence over the config file.
Does any argparse
other similar tool have the ability to determine if a parameter was set when it fell to its default value or was explicitly set by the user?
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Don't include a default if it just complicates things:
parser.add_argument('-p', '--path',
help="The path to a file to read")
And then in your code:
if args.path:
# user specify a value for path
# using -p
pass
elif cfg.path:
# user provided a path in the configuration value
args.path = cfg.path
else:
# no value was specified, use some sort of default value
args.path = DEFAULT_PATH
Or, more compactly:
args.path = next(val for val in
[args.path, cfg.path, DEFAULT_PATH]
if val is not None)
This assumes what cfg.path
will happen None
if no path is specified in the config file. Therefore, if cfg
in fact it is a dictionary, it cfg.get('path')
will do the right thing.
And just for kicks, here's a terrible idea that can tell the difference between using the default and explicitly specifying a value that is the same as the default:
import argparse
class Default(object):
def __init__(self, value):
self.value = value
def __str__(self):
return str(self.value)
DEFAULT_PATH = Default('/some/path')
def parse_args():
p = argparse.ArgumentParser()
p.add_argument('--path', '-p',
default=DEFAULT_PATH)
return p.parse_args()
def main():
args = parse_args()
if args.path is DEFAULT_PATH:
print 'USING DEFAULT'
else:
print 'USING EXPLICIT'
print args.path
if __name__ == '__main__':
main()
Please note: I really don't think this is a good idea.
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