Parse Arguments in Python

This is first time to use Python in seriously. Just start from code snippets used in my projects. Good or bad, it is just a start.

First code snippet

Let’s see the first code snippet. Sounds like it is trying to parse arguments passed into the script.

import sys
from base_utils import get_args

##### initialization #####
globals().update(vars(get_args(sys.argv)))
args = {}
if script_args:
    for entry in script_args:
        key, val = entry.split("=")
        args[key] = val

globals().update(args)

Annotating the code snippet

import

First thing first, the import key word, per the Python tutorial modules, imports a standard module sys and a function get_args from a package (module). There are 2 recommended ways for importing:

• Import a module via import item or import item.subitem.subsubitem, where each item except for the last must be a package; the last item can be a module or a package but cannot be a class or function or variable defined in the previous item.
• Import a module, function, class or variable via from package import item, where the import statement first tests whether the item is defined in the package; if not, it assumes it is a module and attempts to load it. If it fails to find it, an ImportError exception is raised.

sys.argv

The sys.argv variable returns a list of command line arguments passed to a Python script.

argv[0] is the script name (it is operating system dependent whether this is a full pathname or not). If the command was executed using the -c command line option to the interpreter, argv[0] is set to the string '-c'. If no script name was passed to the Python interpreter, argv[0] is the empty string.

get_args()

This is an utility function for parsing arguments. It is defined in the base_utils module.

import argparse
import sys

def get_args(args):
    '''
    Helper function for parsing arguments
    Usage:
        args = get_args(sys.argv)
    '''
    old_argv = sys.argv
    sys.argv = args

    parser = argparse.ArgumentParser(
                description = 'Process arguments for each script/runner')
    # connection arguments
    # serial
    parser.add_argument('-s', '--serial', dest = 'serial',
                        help = 'Device serial')
    # ADB server port
    parser.add_argument('--adb-server-port', dest = 'adb_server_port',
                        help = 'Port for ADB server')
    # ADB local port for uiautomator
    parser.add_argument('--adb-local-port', dest = 'adb_local_port',
                        help = 'ADB local port for uiautomator')

    # script args
    parser.add_argument('--script-args', dest = 'script_args',
                        help = 'Script arguments', nargs = '+')


    args = parser.parse_args()

    sys.argv = old_argv
    globals().update(vars(args))
    return args

This function uses standard library argparse to add (parser.add_argument()) and parse (parser.parse_args()) arguments.

vars()

vars() is a built-in function. It returns the __dict__ attribute for a module, class, instance, or any other object with a __dict__ attribute.

Where, object.__dict__ is a dictionary or other mapping object used to store an object’s (writable) attributes.

globals().update()

globals() is a built-in function. It returns a dictionary representing the current global symbol table. This is always the dictionary of the current module (inside a function or method, this is the module where it is defined, not the module from which it is called).

dict.update([other]) updates the dictionary with the key/value pairs from other, overwriting existing keys. It returns None.

update() accepts either another dictionary object or an iterable of key/value pairs (as tuples or other iterables of length two). If keyword arguments are specified, the dictionary is then updated with those key/value pairs: d.update(red=1, blue=2).

Trying the code snippet

Copy the code snippet into a file, say parse_arguments.py, and put it in the same sub-directory as base_utils.py. Then we can try it.

.\parse_arguments.py --help
usage: parse_arguments.py [-h] [-s SERIAL] [--adb-server-port ADB_SERVER_PORT]
                          [--adb-local-port ADB_LOCAL_PORT]
                          [--script-args SCRIPT_ARGS [SCRIPT_ARGS ...]]

Process arguments for each script/runner

optional arguments:
  -h, --help            show this help message and exit
  -s SERIAL, --serial SERIAL
                        Device serial
  --adb-server-port ADB_SERVER_PORT
                        Port for ADB server
  --adb-local-port ADB_LOCAL_PORT
                        ADB local port for uiautomator
  --script-args SCRIPT_ARGS [SCRIPT_ARGS ...]
                        Script arguments

See the online demo at here.