Default sub-command, or handling no sub-command with argparse

In argparse, you can specify a default sub-command or handle cases where no sub-command is provided by using the argparse.ArgumentParser.set_defaults() method. This method allows you to specify default values for specific attributes of the parser. You can use it to set a default function or behavior when no sub-command is provided.

Here's an example of how to set a default sub-command or behavior using set_defaults:

import argparse

# Create the top-level parser
parser = argparse.ArgumentParser(description="My CLI Tool")

# Create subparsers for sub-commands
subparsers = parser.add_subparsers(title="Sub-commands")

# Define a function to be called when the 'command1' sub-command is used
def command1_function(args):
    print("Executing command 1")

# Define a function to be called when the 'command2' sub-command is used
def command2_function(args):
    print("Executing command 2")

# Add sub-commands
command1_parser = subparsers.add_parser('command1', help='Execute command 1')
command1_parser.set_defaults(func=command1_function)

command2_parser = subparsers.add_parser('command2', help='Execute command 2')
command2_parser.set_defaults(func=command2_function)

# Set a default sub-command or behavior
parser.set_defaults(func=lambda args: parser.print_help())

# Parse the command-line arguments
args = parser.parse_args()

# Call the function associated with the sub-command or default behavior
args.func(args)

In this example:

1. We create a top-level parser using argparse.ArgumentParser.
2. We create subparsers using add_subparsers to handle different sub-commands ('command1' and 'command2').
3. We define functions (command1_function and command2_function) for each sub-command and use set_defaults to associate the function with its respective sub-command.
4. We use parser.set_defaults() to set a default function that will be called when no sub-command is provided. In this case, it prints the help message.
5. We parse the command-line arguments using parser.parse_args().
6. We call the function associated with the sub-command or the default behavior using args.func(args).

With this setup, if you run the script without specifying a sub-command, it will print the help message by default. If you specify 'command1' or 'command2', it will execute the corresponding function.

Examples

1. "Python argparse default sub-command example" Description: Learn how to set a default sub-command in argparse to execute when no sub-command is provided. Code:

   import argparse
   
   # Create the main argument parser
   parser = argparse.ArgumentParser(description='Main parser')
   
   # Define default sub-command
   parser.set_defaults(func=lambda args: parser.print_help())
   
   # Define sub-command parsers
   subparsers = parser.add_subparsers(title='subcommands')
   
   # Sub-command 1: foo
   foo_parser = subparsers.add_parser('foo', help='foo command')
   foo_parser.set_defaults(func=lambda args: print('foo'))
   
   # Sub-command 2: bar
   bar_parser = subparsers.add_parser('bar', help='bar command')
   bar_parser.set_defaults(func=lambda args: print('bar'))
   
   # Parse arguments and execute the appropriate sub-command
   args = parser.parse_args()
   args.func(args)
   

2. "Python argparse handling no sub-command" Description: Understand how to handle cases when no sub-command is provided using argparse. Code:

   import argparse
   
   # Create the main argument parser
   parser = argparse.ArgumentParser(description='Main parser')
   
   # Define default behavior when no sub-command is provided
   def default_action(args):
       parser.print_help()
   
   parser.set_defaults(func=default_action)
   
   # Define sub-command parsers
   subparsers = parser.add_subparsers(title='subcommands')
   
   # Sub-command 1: foo
   foo_parser = subparsers.add_parser('foo', help='foo command')
   foo_parser.set_defaults(func=lambda args: print('foo'))
   
   # Sub-command 2: bar
   bar_parser = subparsers.add_parser('bar', help='bar command')
   bar_parser.set_defaults(func=lambda args: print('bar'))
   
   # Parse arguments and execute the appropriate sub-command
   args = parser.parse_args()
   args.func(args)
   

3. "Python argparse default sub-command handling" Description: Explore how to handle the scenario when no sub-command is specified using argparse with a default sub-command. Code:

   import argparse
   
   # Create the main argument parser
   parser = argparse.ArgumentParser(description='Main parser')
   
   # Define default sub-command
   def default_action(args):
       parser.print_help()
   
   parser.set_defaults(func=default_action)
   
   # Define sub-command parsers
   subparsers = parser.add_subparsers(title='subcommands')
   
   # Sub-command 1: foo
   foo_parser = subparsers.add_parser('foo', help='foo command')
   foo_parser.set_defaults(func=lambda args: print('foo'))
   
   # Sub-command 2: bar
   bar_parser = subparsers.add_parser('bar', help='bar command')
   bar_parser.set_defaults(func=lambda args: print('bar'))
   
   # Parse arguments and execute the appropriate sub-command
   args = parser.parse_args()
   args.func(args)
   

4. "Python argparse default sub-command handling example" Description: Learn how to handle the absence of a sub-command using argparse and execute a default action. Code:

   import argparse
   
   # Create the main argument parser
   parser = argparse.ArgumentParser(description='Main parser')
   
   # Define default action when no sub-command is provided
   def default_action(args):
       parser.print_help()
   
   parser.set_defaults(func=default_action)
   
   # Define sub-command parsers
   subparsers = parser.add_subparsers(title='subcommands')
   
   # Sub-command 1: foo
   foo_parser = subparsers.add_parser('foo', help='foo command')
   foo_parser.set_defaults(func=lambda args: print('foo'))
   
   # Sub-command 2: bar
   bar_parser = subparsers.add_parser('bar', help='bar command')
   bar_parser.set_defaults(func=lambda args: print('bar'))
   
   # Parse arguments and execute the appropriate sub-command or default action
   args = parser.parse_args()
   args.func(args)
   

5. "Python argparse handling no sub-command with default action" Description: Understand how to handle cases when no sub-command is provided using argparse and execute a default action. Code:

   import argparse
   
   # Create the main argument parser
   parser = argparse.ArgumentParser(description='Main parser')
   
   # Define default action when no sub-command is provided
   def default_action(args):
       parser.print_help()
   
   parser.set_defaults(func=default_action)
   
   # Define sub-command parsers
   subparsers = parser.add_subparsers(title='subcommands')
   
   # Sub-command 1: foo
   foo_parser = subparsers.add_parser('foo', help='foo command')
   foo_parser.set_defaults(func=lambda args: print('foo'))
   
   # Sub-command 2: bar
   bar_parser = subparsers.add_parser('bar', help='bar command')
   bar_parser.set_defaults(func=lambda args: print('bar'))
   
   # Parse arguments and execute the appropriate sub-command or default action
   args = parser.parse_args()
   args.func(args)
   

6. "Python argparse default sub-command handling without subparsers" Description: Explore how to handle the absence of sub-commands using argparse without defining subparsers explicitly. Code:

   import argparse
   
   # Create the main argument parser
   parser = argparse.ArgumentParser(description='Main parser')
   
   # Define default action when no sub-command is provided
   def default_action(args):
       parser.print_help()
   
   parser.set_defaults(func=default_action)
   
   # Parse arguments and execute the appropriate sub-command or default action
   args = parser.parse_args()
   
   # Add more logic to determine the default action based on args if needed
   args.func(args)
   

7. "Python argparse default sub-command handling with main parser" Description: Learn how to handle the absence of sub-commands using argparse with a default action defined for the main parser. Code:

   import argparse
   
   # Create the main argument parser
   parser = argparse.ArgumentParser(description='Main parser')
   
   # Define default action when no sub-command is provided
   def default_action(args):
       parser.print_help()
   
   parser.set_defaults(func=default_action)
   
   # Parse arguments and execute the appropriate sub-command or default action
   args = parser.parse_args()
   
   # Add more logic to determine the default action based on args if needed
   args.func(args)
   

8. "Python argparse default sub-command handling without explicit subparsers" Description: Understand how to handle cases when no sub-command is provided using argparse without explicitly defining subparsers. Code:

   import argparse
   
   # Create the main argument parser
   parser = argparse.ArgumentParser(description='Main parser')
   
   # Define default action when no sub-command is provided
   def default_action(args):
       parser.print_help()
   
   parser.set_defaults(func=default_action)
   
   # Parse arguments and execute the appropriate sub-command or default action
   args = parser.parse_args()
   
   # Add more logic to determine the default action based on args if needed
   args.func(args)
   

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