argparse.r2py

"""
<Program Name>
  argparse.r2py

<Started>
  April 27, 2009

<Author>
  n2k8000@u.washington.edu
  Konstantin Pik

<Purpose>
  Parse command line arguments.
  Arguments may be bool (True if the option is given),
      int (name followed by value), or
      str (name followed by value).
  Option names are case-sensitive, free-form string words, e.g.
      --gnu-option, -xoption, anoption

  The default value for missing variables is False, which you may override.

<Note>
  Handling of default values and exceptions is very ad-hoc, and 
  should rather follow the examples of Python's argparse, getopt, etc.

<Sample Usage>
  argparse_scan_bool(callargs, '--local')
    returns False if no --local flag is set
    returns True if --local flag is set
  argparse_scan_str(callargs, '-ip')
    returns False if no -ip flag
    returns string containing ip (parameter following -ip flag)
  argparse_scan_int(callargs, '/port')
    returns False if no /port flag is set
    returns the int following the flag (if any)
"""

class ArgparseError(RepyException):
  """This is raised when we encounter logical errors while parsing"""



def argparse_scan_bool(args_list, option, default_value=False):
  """
  <Purpose>
    Check if an option was passed as an argument.

  <Arguments>
    args_list: List of arguments
    option: The option we are looking for
    default_value: The desired default value, initialized to False.
    
  <Exceptions>
    None known.

  <Side Effects>
    None.

  <Returns>
    Returns True if the option was found in the list of arguments.
    Returns default_value if it was not.

  <Sample Usage>
    if argparse_scan_bool(callargs, '--local'): # we have the argument!
      ... your code ...
  """
  if option in args_list:
    return True
  else:
    return default_value



def argparse_scan_str(args_list, option, default_value=False):
  """
  <Purpose>
    Return the value for the given option, or default_value if 
    option is not present.
    Note: The first occurrence of the option takes precedence!

  <Arguments>
    args_list: List of arguments
    option: The option we are looking for
    default_value: The default value, initialized to False.
    
  <Exceptions>
    ArgparseError if the option value is missing after the option name.

  <Side Effects>
    None.

  <Returns>
    If the option exists, return the value directly following it.
    Otherwise, return the default_value.

  <Sample Usage>
    ip = argparse_scan_str(callargs, '--ip'):
    if ip: # we have an IP!
      ... your code ...
  """
  if option not in args_list:
    return default_value

  # Find the first occurrence of option in the args list
  position = args_list.index(option)

  try:
    return args_list[position+1]
  except IndexError:
    raise ArgparseError("Value missing after option '" + option + "'")



def argparse_scan_int(args_list, option, default_value=False):
  """
  <Purpose>
    Return the int value for the given option, or default_value if 
    option is missing.

  <Arguments>
    args_list: List of arguments
    option: The option we are looking for
    default_value: The default value, initialized to False
    
  <Exceptions>
    ArgparseError if the option value is missing after the option name, 
    or cannot be parsed as an int.

  <Side Effects>
    None.

  <Returns>
    If the option exists, return the value directly following it, 
    as an int. Otherwise, return the default_value.

  <Sample Usage>
    temp_port = argparse_scan_port(callargs, 'port'):
    if temp_port: # we have a port!
      port = temp_port
      ... your code ...
  """
  # int options look like str options (``--OPTION VALUE''). 
  # We'll cast VALUE to int later.
  possible_result = argparse_scan_str(args_list, option, default_value=None)

  if possible_result is None:
    return default_value

  # possible_result maybe contains an int now
  try:
    return int(possible_result)
  except ValueError:
    # Couldn't parse to int.
    raise ArgparseError("Option '" + option + "' was followed by '" + 
        str(possible_result) + "' which did not parse as an int.")