Argument Parser
Simple Basic Example
import argparse
import os
def logging_level_type(level):
LOG_LEVELS = ["CRITICAL", "ERROR", "WARNING", "INFO", "DEBUG"]
level.upper()
if level.upper() not in LOG_LEVELS:
raise argparse.ArgumentTypeError("Invalid Argument: %s" % level)
return level.upper()
def readable_path_type(path):
if not os.path.exists(path):
raise argparse.ArgumentTypeError("Path does not exits: %s" % path)
if not os.access(path, os.R_OK):
raise argparse.ArgumentTypeError("Path not readable: %s" % path)
return path
class custom_action(argparse.Action):
def __call__(self, parser, args, values, option_string=None):
values_new = values * 2
setattr(args, self.dest, values_new)
parser = argparse.ArgumentParser(
description="Description of the program",
formatter_class=argparse.RawTextHelpFormatter,
)
# Positional string Argument
parser.add_argument("pos_arg", type=str,
help="Positional Argument [Mandatory]")
# Int Argument
parser.add_argument("--int-arg", type=int, required=True,
help="Integer Argument")
# Path Argument + custom type validation
parser.add_argument("--path-arg", type=readable_path_type, required=False,
help="Integer Argument")
# List of Float Argument
parser.add_argument("--float-list-arg", type=float, nargs='*', default=[1.0, 2.5], required=False,
help="List of float")
# Boolean Argument
parser.add_argument("--boolean-arg", action="store_true", required=False,
help="Boolean Argument [default value to False]")
parser.add_argument("--option", action=argparse.BooleanOptionalAction, default=True,
help="With this single argument: '--option' and '--no-option' arguments are available (python 3.9+)")
# Argument using a custom action method
parser.add_argument("--customint-arg", type=int, default=3, action=custom_action, required=False,
help="Integer Argument with custom action, => WARNING: the action is not applied on the 'default' value")
# Logging Level
parser.add_argument("--logging-level", type=logging_level_type, nargs='?', const="INFO", default="INFO",
help="Logging level: CRITICAL, ERROR, WARNING, INFO [Default] or DEBUG")
args = parser.parse_args()
With parameters as below:
args = parser.parse_args([
"HeyHey!",
"--int-arg", "43",
"--path-arg", "/home/ndejax",
"--float-list-arg", "4.78", "2.3", "4.4",
"--boolean-arg",
"--no-option",
"--customint-arg", "5",
"--logging-level", "WARNing"
])
The args would be:
Namespace(
pos_arg='HeyHey!',
int_arg=43,
path_arg='/home/ndejax',
float_list_arg=[4.78, 2.3, 4.4],
boolean_arg=True,
option=False,
customint_arg=10,
logging_level='WARNING'
)
Note
When using arguments with hyphen characters (-), they are automatically replace by underscore (_) characters in the (args) namespace.
Example Using Sub Parser
import argparse
parser = argparse.ArgumentParser(
description="Example of Argparser with sub parsers",
formatter_class=argparse.RawTextHelpFormatter
)
subparsers = parser.add_subparsers(dest='action_choice', required=True,
help='Action to do'
)
subparser_1 = subparsers.add_parser("read")
subparser_2 = subparsers.add_parser("process")
subparser_3 = subparsers.add_parser("plot")
# Common arguments to each subparsers
for subparser in [subparser_1, subparser_2, subparser_3]:
subparser.add_argument('--inputs', type=str, nargs="*", required=True,
help="Path to process")
subparser.add_argument('--logging-level', nargs="?", const="INFO", type=str, default="INFO",
help="Logging level: CRITICAL, ERROR, WARNING, INFO [Default] or DEBUG")
# Arguments specific to the subparser_1
subparser_1.add_argument('--argument', type=int, required=True,
help="Useless Argument")
# Arguments specific to the subparser_2
subparser_3.add_argument('--output', type=str, required=True,
help="Directory where to save the figures")
# Parse input arguments
args = parser.parse_args()
With parameters as below:
args = parser.parse_args([
"plot",
"--inputs", "/home/file1", "/home/file2", "/home/file3", "/home/file4",
"--output", "/home/output/path",
])
The args would be:
Namespace(
action_choice='plot',
inputs=['/home/file1', '/home/file2', '/home/file3', '/home/file4'],
logging_level='INFO',
output='/home/output/path'
)
Warning
- For common arguments between different subparsers, we could also choose to add the argument on the main parser but it has some drawbacks:
The order of the arguments must be in the right order: main arguments and then subparser arguments.
If the main parser has some list argument the subparser won’t work properly.
(See example below)
import argparse
parser = argparse.ArgumentParser(
description="Example of Argparser with sub parsers",
formatter_class=argparse.RawTextHelpFormatter
)
# Common arguments to each subparsers
parser.add_argument('--inputs', type=str, nargs="*", required=True,
help="Path to process")
parser.add_argument('--logging-level', nargs="?", const="INFO", type=str, default="INFO",
help="Logging level: CRITICAL, ERROR, WARNING, INFO [Default] or DEBUG")
subparsers = parser.add_subparsers(dest='action_choice', required=True,
help='Action to do'
)
subparser_1 = subparsers.add_parser("read")
subparser_2 = subparsers.add_parser("process")
subparser_3 = subparsers.add_parser("plot")
# Arguments specific to the subparser_1
subparser_1.add_argument('--argument', type=int, required=True,
help="Useless Argument")
# Arguments specific to the subparser_2
subparser_3.add_argument('--output', type=str, required=True,
help="Directory where to save the figures")
# Parse input arguments
args = parser.parse_args()
For example, in the parser above, the following input arguments will work properly:
args = parser.parse_args([
"--inputs", "/home/file1", "/home/file2", "/home/file3", "/home/file4",
"--logging-level", "INFO",
"plot",
"--output", "/home/output/path",
])
But, the parser won’t be able to parse the following input arguments:
args = parser.parse_args([
"--inputs", "/home/file1", "/home/file2", "/home/file3", "/home/file4",
# "--logging-level", "INFO",
"plot",
"--output", "/home/output/path",
])
Because the parser consider the plot argument as one of the --inputs item.
Reading the argument from a yaml file
Below is an example of Argument Parser that also accepts arguments using an input yaml parameter file.
import argparse
import yaml
from typing import Union, Dict, List
def convert2ListOfString(params: Union[Dict, List, int, str, float], list_string: List[str]=None) -> List[str]:
if list_string is None:
list_string = []
if isinstance(params, dict):
for key in params.keys():
list_string.append(str(key))
convert2ListOfString(params[key], list_string)
elif isinstance(params, list):
for item in params:
convert2ListOfString(item, list_string)
else:
list_string.append(str(params))
return list_string
class ArgumentParserWithConfigFile(argparse.ArgumentParser):
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
self.config_arg_name = "--config-file"
self.add_argument(self.config_arg_name, type=str, required=False,
help="Config File (parameters defined as input command line will override the parameters set in the config file)")
def config_file_args(self, args: List[str]) -> None:
if self.config_arg_name not in args:
return None
# Extract the argument
ind = args.index(self.config_arg_name)
_ = args.pop(ind)
config_filepath = args.pop(ind)
if len(args) > 0:
self.error("When providing the config file parameters, other arguments must be left out")
# Open the config file
with open(config_filepath, 'r') as f:
cdata = yaml.safe_load(f)
# Copy the parameters from the config file to the args
config_args = convert2ListOfString(cdata)
args.extend(config_args)
def _parse_known_args(self, arg_strings, namespace):
self.config_file_args(arg_strings)
return super()._parse_known_args(arg_strings, namespace)
Warning
You can either use the config file argument alone or use only the other parameters. This implementation does not enable using both at the same time.
Example of use:
parser = ArgumentParserWithConfigFile(
description="Example of Argparser with sub parsers",
formatter_class=argparse.RawTextHelpFormatter
)
subparsers = parser.add_subparsers(dest='action_choice', required=True,
help='Action to do'
)
subparser_read = subparsers.add_parser("read")
subparser_process = subparsers.add_parser("process")
subparser_plot = subparsers.add_parser("plot")
# Common arguments to each subparsers
for subparser in [subparser_read, subparser_process, subparser_plot]:
subparser.add_argument('--inputs', type=str, nargs="*", required=True,
help="Path to process")
subparser.add_argument('--logging-level', nargs="?", const="INFO", type=str, default="INFO",
help="Logging level: CRITICAL, ERROR, WARNING, INFO [Default] or DEBUG")
# Arguments specific to the subparser_read
subparser_read.add_argument('--argument', type=int, required=True,
help="Useless Argument")
# Arguments specific to the subparser_plot
subparser_plot.add_argument('--output', type=str, required=True,
help="Directory where to save the figures")
# Using input arguments
args = parser.parse_args([
"plot",
"--inputs", "/home/file1", "/home/file2", "/home/file3",
"--logging-level", "WARNING",
"--output", "/home/output/path",
])
# Using config file parameters
args = parser.parse_args([
"--config-file", "example.yaml",
])
With example.yaml:
read:
--inputs: [/home/file1, /home/file2, /home/file3]
--logging-level: WARNING
--argument: 8