I am creating a python script and for parsing the arguments I would need this:
the script will accept three parameters, only one always mandatory, the second one will only be mandatory depending on certain values of the first one and the third one may or may not appear.
This is my try:
class pathAction(argparse.Action):
folder = {'remote':'/path1', 'projects':'/path2'}
def __call__(self, parser, args, values, option = None):
args.path = values
print "ferw %s " % args.component
if args.component=='hos' or args.component=='hcr':
print "rte %s" % args.path
if args.path and pathAction.folder.get(args.path):
args.path = pathAction.folder[args.path]
else:
parser.error("You must enter the folder you want to clean: available choices[remote, projects]")
def main():
try:
# Arguments parsing
parser = argparse.ArgumentParser(description="""This script will clean the old component files.""")
parser.add_argument("-c", "--component", help="component to clean", type=lowerit, choices=["hos", "hcr", "mdw", "gui"], required=True)
parser.add_argument("-p", "--path", help="path to clean", action = pathAction, choices = ["remote", "projects"])
parser.add_argument("-d", "--delete", help="parameter for deleting the files from the filesystem", nargs='*', default=True)
args = parser.parse_args()
if works well except one case: if i have -c it should complain because there is no -p however it does not
Can you help me please?
Thanks
You can add some custom validation like this:
if args.component and not args.path:
parser.error('Your error message!')
Your special action will be used only if there is a -p argument. If you just give it a -c the cross check is never used.
Generally checking for interactions after parse_args (as Gohn67 suggested) is more reliable, and simpler than with custom actions.
What happens if your commandline was '-p remote -c ...'? pathAction would be called before the -c value is parsed and set. Is that what you want? Your special action only works if -p is given, and is the last argument.
Another option is to make 'component' a subparser positional. By default positionals are required. path and delete can be added to those subparsers that need them.
import argparse
parser = argparse.ArgumentParser(description="""This script will clean the old component files.""")
p1 = argparse.ArgumentParser(add_help=False)
p1.add_argument("path", help="path to clean", choices = ["remote", "projects"])
p2 = argparse.ArgumentParser(add_help=False)
p2.add_argument("-d", "--delete", help="parameter for deleting the files from the filesystem", nargs='*', default=True)
sp = parser.add_subparsers(dest='component',description="component to clean")
sp.add_parser('hos', parents=[p1,p2])
sp.add_parser('hcr', parents=[p1,p2])
sp.add_parser('mdw', parents=[p2])
sp.add_parser('gui', parents=[p2])
print parser.parse_args()
sample use:
1848:~/mypy$ python2.7 stack21625446.py hos remote -d 1 2 3
Namespace(component='hos', delete=['1', '2', '3'], path='remote')
I used parents to simplify adding arguments to multiple subparsers. I made path a positional, since it is required (for 2 of the subparsers). In those cases --path just makes the user type more. With nargs='*', --delete has to belong to the subparsers so it can occur last. If it's nargs was fixed (None or number) it could be an argument of parser.
Related
I realize the title might be confusing, but I didn't know how to word my problem.
My program's command line syntax looks like this:
conv.py val from to, where to is optional, but I don't think that should matter.
I'm trying to add a flag that forces my program to ignore cached data and update its database. It should work like this:
conv.py -f val from to
but also like this:
conv.py -f
I know it should be possible to do this because the inbuilt -h flag in argparse works in a similar manner where you can say conv.py val from to or conv.py -h or conv.py -h val. However, I am at a loss as to how to achieve this.
My current code just has the -f flag as an optional argument:
def parse_args():
parser = argparse.ArgumentParser(prog='conv')
parser.add_argument('-f', action='store_true')
parser.add_argument('value')
parser.add_argument('from_', metavar='from' )
parser.add_argument('to', nargs='?', default='neg')
args = parser.parse_args()
return args.from_, args.to, args.value, args.f
I would like to make it so the presence of the -f flag is acceptable by itself or with all the other arguments. Any help is appreciated.
To do that you would create a custom action which exits the parsing:
import argparse
class MyAction(argparse.Action):
def do_the_thing(self):
print("hello from my action")
def __call__(self, parser, namespace, values, option_string=None):
self.do_the_thing()
parser.exit()
parser = argparse.ArgumentParser()
parser.add_argument('value')
parser.add_argument('from_', metavar='from' )
parser.add_argument('to', nargs='?', default='neg')
parser.add_argument("-f", nargs=0, action=MyAction)
args = parser.parse_args()
print("after args parsed")
Now if -f was passed, then print("after args parsed") will not be reached regardless of whether required arguments were sent or not. You may access the parser namespace from within the action instance.
In argparse, I want to prevent a particular combination of arguments. Lets see the sample code.
Sample:
import argparse
parser = argparse.ArgumentParser(add_help=False)
parser.add_argument('--firstname', dest='fn', action='store')
parser.add_argument('--lastname', dest='ln', action='store')
parser.add_argument('--fullname', dest='full', action='store')
args = parser.parse_args()
For eg: --firstname --lastname --fullname
The user can run the code in 2 days.
Way 1:
code.py --firstname myfirst --lastname mylast
Way 2:
code.py --fullname myfullname
Prevent
We should not use the combination fistname, fullname or lastname, fullname. If we use both, then it should not execute.
Can someone help me to fix this?
Not sure that is an argparse specific behavior that is possible. But as long as those items are going to their own variables in the argparse resposes its a simple set of programming to check which ones are set and issue a message and exit.
example (assuming the result of parsing is in argsvalue):
if argsvalue.fullname and (argsvalue.firstname or argsvalue.lastname):
print ("missuse of name options.....")
This assumes the argparse default for the vars is None (then if anything is set in them they will test to true with the logic above...
Like this answer proposes (on a similar question) you can do something like the following by using subparsers for both cases:
# create the top-level parser
parser = argparse.ArgumentParser(add_help=false)
subparsers = parser.add_subparsers(help='help for subcommands')
# create the parser for the "full_name" command
full_name = subparsers.add_parser('full_name', help='full_name help')
full_name.add_argument('--fullname', dest='full', action='store')
# create the parser for the "separate_names" command
separate_names = subparsers.add_parser('separate_names', help='separate_names help')
separate_names.add_argument('--firstname', dest='fn', action='store')
separate_names.add_argument('--lastname', dest='ln', action='store')
args = parser.parse_args()
You can improve it even further by requiring both the first and last name of the user as it generally makes sense.
You can split your arguments into separate commands and use subparsers, for example:
import argparse
parser = argparse.ArgumentParser()
subparsers = parser.add_subparsers()
parser_clean = subparsers.add_parser('clean', description='clean build folder')
parser_clean.add_argument('--all', help='clean build folder and logs', action='store_true')
parser_deploy = subparsers.add_parser('deploy')
parser_deploy.add_argument('object')
parser_deploy.add_argument('--nc', help='no cleanup', action='store_true')
args = parser.parse_args()
I have the following
import argparse
parser = argparse.ArgumentParser(prog='macc', usage='macc [options] [address]')
parser.add_argument('-l', '--list', help='Lists MAC Addresses')
args = parser.parse_args()
print(args)
def list_macs():
print("Found the following MAC Addresses")
I get an error when running with python macc.py -l it says that an argument was expected. Even when I change my code to parser.add_argument('-l', '--list', help='Lists MAC Addresses' default=1) I get the same error.
The default action for an argument is store, which sets the value of the attribute in the namespace returned by parser.parse_args using the next command line argument.
You don't want to store any particular value; you just want to acknowledge that -l was used. A quick hack would be to use the store_true action (which would set args.list to True).
parser = argparse.ArgumentParser(prog='macc')
parser.add_argument('-l', '--list', action='store_true', help='Lists MAC Addresses')
args = parser.parse_args()
if args.list:
list_macs()
The store_true action implies type=bool and default=False as well.
However, a slightly cleaner approach would be to define a subcommand named list. With this approach, your invocation would be macc.py list rather than macc.py --list.
parser = argparse.ArgumentParser(prog='macc')
subparsers = parser.add_subparsers(dest='cmd_name')
subparsers.add_parser('list')
args = parser.parse_args()
if args.cmd_name == "list":
list_macs()
If you use the argument -l on the cli you need to specify an argument, like:
python macc.py -l something
If you set default = 1 on the -l argument you can run your script without using it like this:
python macc.py
I've read this http://docs.python.org/release/2.6.2/library/optparse.html
But I'm not so clear how to make an option to be required in optparse?
I've tried to set "required=1" but I got an error:
invalid keyword arguments: required
I want to make my script require --file option to be input by users. I know that the action keyword gives you error when you don't supply value to --file whose action="store_true".
You can implement a required option easily.
parser = OptionParser(usage='usage: %prog [options] arguments')
parser.add_option('-f', '--file',
dest='filename',
help='foo help')
(options, args) = parser.parse_args()
if not options.filename: # if filename is not given
parser.error('Filename not given')
Since if not x doesn't work
for some(negative,zero) parameters,
and to prevent lots of if tests,
i preferr something like this:
required="host username password".split()
parser = OptionParser()
parser.add_option("-H", '--host', dest='host')
parser.add_option("-U", '--user', dest='username')
parser.add_option("-P", '--pass', dest='password')
parser.add_option("-s", '--ssl', dest='ssl',help="optional usage of ssl")
(options, args) = parser.parse_args()
for r in required:
if options.__dict__[r] is None:
parser.error("parameter %s required"%r)
On the help message of each required variable Im writting a '[REQUIRED]' string at the beggining, to tag it to be parsed later, then I can simply use this function to wrap it around:
def checkRequiredArguments(opts, parser):
missing_options = []
for option in parser.option_list:
if re.match(r'^\[REQUIRED\]', option.help) and eval('opts.' + option.dest) == None:
missing_options.extend(option._long_opts)
if len(missing_options) > 0:
parser.error('Missing REQUIRED parameters: ' + str(missing_options))
parser = OptionParser()
parser.add_option("-s", "--start-date", help="[REQUIRED] Start date")
parser.add_option("-e", "--end-date", dest="endDate", help="[REQUIRED] End date")
(opts, args) = parser.parse_args(['-s', 'some-date'])
checkRequiredArguments(opts, parser)
The current answer with the most votes would not work if, for example, the argument were an integer or float for which zero is a valid input. In these cases it would say that there is an error. An alternative (to add to the several others here) would be to do e.g.
parser = OptionParser(usage='usage: %prog [options] arguments')
parser.add_option('-f', '--file', dest='filename')
(options, args) = parser.parse_args()
if 'filename' not in options.__dict__:
parser.error('Filename not given')
I'm forced to use python 2.6 for our solution so I'm stick to optparse module.
Here is solution I found to check for required options that works without specifying second time list of required options. Thus when you add new option you don't have to add it's name into the list of options to check.
My criteria for required option - option value should be not None and this options doesn't have default (user didn't specified add_option(default="...",...).
def parse_cli():
"""parse and check command line options, shows help message
#return: dict - options key/value
"""
import __main__
parser = OptionParser(description=__main__.__doc__)
parser.add_option("-d", "--days", dest="days",
help="Number of days to process")
parser.add_option("-p", "--period", dest="period_length",default="2",
help="number or hours per iteration, default value=%default hours")
(options, args) = parser.parse_args()
"""get dictionary of options' default values.
in this example: { 'period_length': '2','days': None}"""
defaults = vars(parser.get_default_values())
optionsdict = vars(options)
all_none = False
for k,v in optionsdict.items():
if v is None and defaults.get(k) is None:
all_none = True
if all_none:
parser.print_help()
sys.exit()
return optionsdict
There are at least two methods of implementing required options with optparse. As mentioned in the docs page, optparse doesn’t prevent you from implementing required options, but doesn’t give you much help at it either. Find below the examples found in files distributed with the source.
Although please note that optparse module is deprecated since version 2.7 and will not be developed further. You should use argparse module instead.
Version 1: Add a method to OptionParser which applications must call after parsing arguments:
import optparse
class OptionParser (optparse.OptionParser):
def check_required (self, opt):
option = self.get_option(opt)
# Assumes the option's 'default' is set to None!
if getattr(self.values, option.dest) is None:
self.error("%s option not supplied" % option)
parser = OptionParser()
parser.add_option("-v", action="count", dest="verbose")
parser.add_option("-f", "--file", default=None)
(options, args) = parser.parse_args()
print "verbose:", options.verbose
print "file:", options.file
parser.check_required("-f")
Source: docs/lib/required_1.txt
Version 2: Extend Option and add a required attribute; extend OptionParser to ensure that required options are present after parsing:
import optparse
class Option (optparse.Option):
ATTRS = optparse.Option.ATTRS + ['required']
def _check_required (self):
if self.required and not self.takes_value():
raise OptionError(
"required flag set for option that doesn't take a value",
self)
# Make sure _check_required() is called from the constructor!
CHECK_METHODS = optparse.Option.CHECK_METHODS + [_check_required]
def process (self, opt, value, values, parser):
optparse.Option.process(self, opt, value, values, parser)
parser.option_seen[self] = 1
class OptionParser (optparse.OptionParser):
def _init_parsing_state (self):
optparse.OptionParser._init_parsing_state(self)
self.option_seen = {}
def check_values (self, values, args):
for option in self.option_list:
if (isinstance(option, Option) and
option.required and
not self.option_seen.has_key(option)):
self.error("%s not supplied" % option)
return (values, args)
parser = OptionParser(option_list=[
Option("-v", action="count", dest="verbose"),
Option("-f", "--file", required=1)])
(options, args) = parser.parse_args()
print "verbose:", options.verbose
print "file:", options.file
Source: docs/lib/required_2.txt
I'm also stuck on python 2.6 (pining for python2.7 and argparse, which not only has required arguments, but lets me specify that one of a set must be supplied); my approach requires a second pass, but lets me prompt for missing arguments unless running in batch mode:
# from myscript
import helpers
import globalconfig
parser = optparse.OptionParser(usage=myheader,epilog=myfooter)
parser.add_option("-L","--last",
action="store",dest="last_name",default="",
help="User's last (family) name; prompted for if not supplied"
)
parser.add_option("-y","--yes",
action="store_true",dest="batch_flag",default=False,
help="don't prompt to confirm actions (batch mode)"
)
[...]
(options, args) = parser.parse_args()
globalconfig.batchmode = options.batch_flag
[...]
last = prompt_if_empty(options.last_name,
"Last name (can supply with \"-L\" or \"--last\" option):")
# from helpers.py
def prompt_if_empty(variable,promptstring):
if not variable:
if globalconfig.batchmode:
raise Exception('Required variable missing.')
print "%s" %promptstring
variable = raw_input(globalconfig.prompt)
return variable
(I'm thinking of making my own parser class that has common options for global configs baked in.)
Another answer to this question cited parser.error, which I was unfamiliar with when I wrote the code, but might have been a better choice.
As the optparse module is deprecated since version 2.7, you will probably find some more up to date examples here: Dead simple argparse example wanted: 1 argument, 3 results
I would use argparse library that has this functionality embedded:
PARSER.add_argument("-n", "--namespace", dest="namespace", required=True,
help="The path within the repo to the data base")
argparse reference
Assume I have a program that uses argparse to process command line arguments/options. The following will print the 'help' message:
./myprogram -h
or:
./myprogram --help
But, if I run the script without any arguments whatsoever, it doesn't do anything. What I want it to do is to display the usage message when it is called with no arguments. How is that done?
This answer comes from Steven Bethard on Google groups. I'm reposting it here to make it easier for people without a Google account to access.
You can override the default behavior of the error method:
import argparse
import sys
class MyParser(argparse.ArgumentParser):
def error(self, message):
sys.stderr.write('error: %s\n' % message)
self.print_help()
sys.exit(2)
parser = MyParser()
parser.add_argument('foo', nargs='+')
args = parser.parse_args()
Note that the above solution will print the help message whenever the error
method is triggered. For example, test.py --blah will print the help message
too if --blah isn't a valid option.
If you want to print the help message only if no arguments are supplied on the
command line, then perhaps this is still the easiest way:
import argparse
import sys
parser=argparse.ArgumentParser()
parser.add_argument('foo', nargs='+')
if len(sys.argv)==1:
parser.print_help(sys.stderr)
sys.exit(1)
args=parser.parse_args()
Note that parser.print_help() prints to stdout by default. As init_js suggests, use parser.print_help(sys.stderr) to print to stderr.
Instead of writing a class, a try/except can be used instead
try:
options = parser.parse_args()
except:
parser.print_help()
sys.exit(0)
The upside is that the workflow is clearer and you don't need a stub class. The downside is that the first 'usage' line is printed twice.
This will need at least one mandatory argument. With no mandatory arguments, providing zero args on the commandline is valid.
With argparse you could use ArgumentParser.print_usage():
parser.argparse.ArgumentParser()
# parser.add_args here
# sys.argv includes a list of elements starting with the program
if len(sys.argv) < 2:
parser.print_usage()
sys.exit(1)
Printing help
ArgumentParser.print_usage(file=None)
Print a brief description of how the ArgumentParser should be invoked on the command line. If file is None, sys.stdout is assumed.
The cleanest solution will be to manually pass default argument if none were given on the command line:
parser.parse_args(args=None if sys.argv[1:] else ['--help'])
Complete example:
import argparse, sys
parser = argparse.ArgumentParser()
parser.add_argument('--host', default='localhost', help='Host to connect to')
# parse arguments
args = parser.parse_args(args=None if sys.argv[1:] else ['--help'])
# use your args
print("connecting to {}".format(args.host))
This will print complete help (not short usage) if called w/o arguments.
If you associate default functions for (sub)parsers, as is mentioned under add_subparsers, you can simply add it as the default action:
parser = argparse.ArgumentParser()
parser.set_defaults(func=lambda x: parser.print_usage())
args = parser.parse_args()
args.func(args)
Add the try-except if you raise exceptions due to missing positional arguments.
If you have arguments that must be specified for the script to run - use the required parameter for ArgumentParser as shown below:-
parser.add_argument('--foo', required=True)
parse_args() will report an error if the script is run without any arguments.
Throwing my version into the pile here:
import argparse
parser = argparse.ArgumentParser()
args = parser.parse_args()
if not vars(args):
parser.print_help()
parser.exit(1)
You may notice the parser.exit - I mainly do it like that because it saves an import line if that was the only reason for sys in the file...
There are a pair of one-liners with sys.argv[1:] (a very common Python's idiom to refer the command line arguments, being sys.argv[0] the script's name) that can do the job.
The first one is self-explanatory, clean and pythonic:
args = parser.parse_args(None if sys.argv[1:] else ['-h'])
The second one is a little hackier. Combining the previously evaluated fact that an empty list is False with the True == 1 and False == 0 equivalences you get this:
args = parser.parse_args([None, ['-h']][not sys.argv[1:]])
Maybe too many brackets, but pretty clear if a previous argument selection was made.
_, *av = sys.argv
args = parser.parse_args([None, ['-h']][not av])
parser.print_help()
parser.exit()
The parser.exit method also accept a status (returncode), and a message value (include a trailing newline yourself!).
an opinionated example,
:)
#!/usr/bin/env python3
""" Example argparser based python file
"""
import argparse
ARGP = argparse.ArgumentParser(
description=__doc__,
formatter_class=argparse.RawTextHelpFormatter,
)
ARGP.add_argument('--example', action='store_true', help='Example Argument')
def main(argp=None):
if argp is None:
argp = ARGP.parse_args() # pragma: no cover
if 'soemthing_went_wrong' and not argp.example:
ARGP.print_help()
ARGP.exit(status=64, message="\nSomething went wrong, --example condition was not set\n")
if __name__ == '__main__':
main() # pragma: no cover
Example calls:
$ python3 ~/helloworld.py; echo $?
usage: helloworld.py [-h] [--example]
Example argparser based python file
optional arguments:
-h, --help show this help message and exit
--example Example Argument
Something went wrong, --example condition was not set
64
$ python3 ~/helloworld.py --example; echo $?
0
Most of the answers here required another module, such as sys, to be imported or were using optional arguments. I wanted to discover an answer that used only argparse, worked with required arguments, and if possible worked without catching exceptions. I ended up with the following:
import argparse
if __name__ == '__main__':
arg_parser = argparse.ArgumentParser(add_help=False)
arg_parser.add_argument('input_file', type=str, help='The path to the input file.')
arg_parser.add_argument('output_file', type=str, help='The path to the output file.')
arg_parser.add_argument('-h','--help', action='store_true', help='show this help message and exit')
arg_parser.usage = arg_parser.format_help()
args = arg_parser.parse_args()
The main idea was to use the format_help function in order to provide the help string to the usage statement. Setting add_help to False in the call to ArgumentParser() prevents the help statement from printing twice in certain circumstances. However, I had to create an argument for the optional help argument that mimicked the typical help message once it was set to False in order to display the optional help argument in the help message. The action is set to store_true in the help argument to prevent the help message from filling in a value like HELP for the parameter when it prints the help message.
So for a really simple answer. Most of the time with argparse you are checking to see if parameters are set anyway, to call a function that does something.
If no parameters, just else out at the end and print the help. Simple and works.
import argparse
import sys
parser = argparse.ArgumentParser()
group = parser.add_mutually_exclusive_group()
group.add_argument("--holidays", action='store_true')
group.add_argument("--people", action='store_true')
args=parser.parse_args()
if args.holidays:
get_holidays()
elif args.people:
get_people()
else:
parser.print_help(sys.stderr)
Here is another way to do it, if you need something flexible where you want to display help if specific params are passed, none at all or more than 1 conflicting arg:
import argparse
import sys
def main():
parser = argparse.ArgumentParser()
parser.add_argument('-d', '--days', required=False, help="Check mapped inventory that is x days old", default=None)
parser.add_argument('-e', '--event', required=False, action="store", dest="event_id",
help="Check mapped inventory for a specific event", default=None)
parser.add_argument('-b', '--broker', required=False, action="store", dest="broker_id",
help="Check mapped inventory for a broker", default=None)
parser.add_argument('-k', '--keyword', required=False, action="store", dest="event_keyword",
help="Check mapped inventory for a specific event keyword", default=None)
parser.add_argument('-p', '--product', required=False, action="store", dest="product_id",
help="Check mapped inventory for a specific product", default=None)
parser.add_argument('-m', '--metadata', required=False, action="store", dest="metadata",
help="Check mapped inventory for specific metadata, good for debugging past tix", default=None)
parser.add_argument('-u', '--update', required=False, action="store_true", dest="make_updates",
help="Update the event for a product if there is a difference, default No", default=False)
args = parser.parse_args()
days = args.days
event_id = args.event_id
broker_id = args.broker_id
event_keyword = args.event_keyword
product_id = args.product_id
metadata = args.metadata
make_updates = args.make_updates
no_change_counter = 0
change_counter = 0
req_arg = bool(days) + bool(event_id) + bool(broker_id) + bool(product_id) + bool(event_keyword) + bool(metadata)
if not req_arg:
print("Need to specify days, broker id, event id, event keyword or past tickets full metadata")
parser.print_help()
sys.exit()
elif req_arg != 1:
print("More than one option specified. Need to specify only one required option")
parser.print_help()
sys.exit()
# Processing logic here ...
Cheers!
I like to keep things as simple as possible, this works great:
#!/usr/bin/env python3
Description = """Tool description"""
Epilog = """toolname.py -a aflag -b bflag with these combined it does blah"""
arg_parser = argparse.ArgumentParser(
formatter_class=argparse.RawDescriptionHelpFormatter,
description=Description,
epilog=Epilog,
)
try:
if len(sys.argv) == 1:
arg_parser.print_help()
except Exception as e:
print(e)
This is how I start all my tools as its always good to include some examples
When call add_subparsers method save the first positional argument to dest= and check value after argparse has been initialized, like this:
subparsers = parser.add_subparsers(dest='command')
And just check this this variable:
if not args.command:
parser.print_help()
parser.exit(1) # If exit() - exit code will be zero (no error)
Full example:
#!/usr/bin/env python
""" doc """
import argparse
import sys
parser = argparse.ArgumentParser(description=__doc__)
subparsers = parser.add_subparsers(dest='command',
help='List of commands')
list_parser = subparsers.add_parser('list',
help='List contents')
list_parser.add_argument('dir', action='store',
help='Directory to list')
create_parser = subparsers.add_parser('create',
help='Create a directory')
create_parser.add_argument('dirname', action='store',
help='New directory to create')
create_parser.add_argument('--read-only', default=False, action='store_true',
help='Set permissions to prevent writing to the directory')
args = parser.parse_args()
if not args.command:
parser.print_help()
parser.exit(1)
print(vars(args)) # For debug
This approach is a lot more elegant than most others. Instead of overriding error(), you can control the behaviour a lot more precisely by wrapping the parse_args() method:
import sys
import argparse
HelpFlags = ('help', '--help', '-h', '/h', '?', '/?', )
class ArgParser (argparse.ArgumentParser):
def __init__(self, *args, **kws):
super().__init__(*args, **kws)
def parse_args(self, args=None, namespace=None):
if args is None:
args = sys.argv[1:]
if len(args) < 1 or (args[0].lower() in HelpFlags):
self.print_help(sys.stderr)
sys.exit()
return super().parse_args(args, namespace)
Set your positional arguments with nargs, and check if positional args are empty.
import argparse
parser = argparse.ArgumentParser()
parser.add_argument('file', nargs='?')
args = parser.parse_args()
if not args.file:
parser.print_help()
Reference Python nargs
If your command is something where a user needs to choose some action, then use a mutually exclusive group with required=True.
This is kind of an extension to the answer given by pd321.
import argparse
parser = argparse.ArgumentParser()
group = parser.add_mutually_exclusive_group(required=True)
group.add_argument("--batch", action='store', type=int, metavar='pay_id')
group.add_argument("--list", action='store_true')
group.add_argument("--all", action='store_true', help='check all payments')
args=parser.parse_args()
if args.batch:
print('batch {}'.format(args.batch))
if args.list:
print('list')
if args.all:
print('all')
Output:
$ python3 a_test.py
usage: a_test.py [-h] (--batch pay_id | --list | --all)
a_test.py: error: one of the arguments --batch --list --all is required
This only give the basic help. And some of the other answers will give you the full help. But at least your users know they can do -h
This isn't good (also, because intercepts all errors), but:
def _error(parser):
def wrapper(interceptor):
parser.print_help()
sys.exit(-1)
return wrapper
def _args_get(args=sys.argv[1:]):
parser = argparser.ArgumentParser()
parser.error = _error(parser)
parser.add_argument(...)
...
Here is definition of the error function of the ArgumentParser class.
As you see, the following signature takes two arguments. However, functions outside the class know nothing about first argument self, because, roughly speaking, this argument is for the class.
def _error(self, message):
self.print_help()
sys.exit(-1)
def _args_get(args=sys.argv[1:]):
parser = argparser.ArgumentParser()
parser.error = _error
...
will output:
"AttributeError: 'str' object has no attribute 'print_help'"
You can pass parser (self) in _error function, by calling it:
def _error(self, message):
self.print_help()
sys.exit(-1)
def _args_get(args=sys.argv[1:]):
parser = argparser.ArgumentParser()
parser.error = _error(parser)
...
But if you don't want exit the program right now, return it:
def _error(parser):
def wrapper():
parser.print_help()
sys.exit(-1)
return wrapper
Nonetheless, parser doesn't know that it has been modified. Thus, when an error occurs, it will print the cause of it (by the way, it's a localized translation). So intercept it:
def _error(parser):
def wrapper(interceptor):
parser.print_help()
sys.exit(-1)
return wrapper
Now, when an error occurs, parser will print the cause of it, and you'll intercept it, look at it, and... throw out.