Uncategorized | MacLochlainns Weblog

A couple of my students wanted me to write a switch and parameter handler for Python scripts. I wrote it just to show them it’s possible but I also show them how to do it correctly with the Python getopt library, which was soft-deprecated in Python 3.13 and replaced by the Python argparse library. The debate is which one I show you first in the blog.

This is the getops.py script that uses Python’s getopt library. There is a small trick to the options and long options values. You append a colon (:) to the option when it has a value, and append an equal (=) to the long option when it has a value.

#!/usr/bin/python
 
# Import libraries.
import getopt, sys
import mysql.connector
from mysql.connector import errorcode
 
# Define local function.
def help():
 
  # Declare display string.
  display = \
""" Program Help
+---------------+-------------+-------------------+
| -h  --help    |             | Help switch.      |
| -o  --output  | output_file | Output file name. |
| -q  --query   | query_file  | Query file name.  |
| -v  --verbose |             | Verbose switch.   |
+---------------+-------------+-------------------+"""
 
  # Return string.
  return display
 
# ============================================================
#  Set local variables for switch and parameter placeholders.
# ============================================================
display = False
log = []
output_file = ''
query_file = ''
verbose = False
 
opts = "ho:q:v"
long_opts = ["help","output=","query=","verbose"]
 
# ============================================================
#  Capture argument list minus the program name.
# ============================================================
args = sys.argv[1:]
 
# ============================================================
#  Use a try-except block.
# ============================================================
try:
  # Assign the results of the getopt function.
  params, values = getopt.getopt(args, opts, long_opts)
 
  # Loop through the parameters.
  for curr_param, curr_value in params:
    if curr_param in ("-h","--help"):
      print(help())
    elif curr_param in ("-o","--output"):
      output_file = curr_value
    elif curr_param in ("-q","--query"):
      query_file = curr_value
    elif curr_param in ("-v","--verbose"):
      verbose = True
 
    # Append entry to log.
    log.append('[' + curr_param + '][' + curr_value + ']')
 
  # Print verbose parameter handling.
  if verbose:
    print(" Parameter Diagnostics\n-------------------------")
    for i in log: print(i)
 
# Exception block.
except getopt.GetoptError as e:
  # output error, and return with an error code
  print (str(e))

#!/usr/bin/python # Import libraries. import getopt, sys import mysql.connector from mysql.connector import errorcode # Define local function. def help(): # Declare display string. display = \ """ Program Help +---------------+-------------+-------------------+ | -h --help | | Help switch. | | -o --output | output_file | Output file name. | | -q --query | query_file | Query file name. | | -v --verbose | | Verbose switch. | +---------------+-------------+-------------------+""" # Return string. return display # ============================================================ # Set local variables for switch and parameter placeholders. # ============================================================ display = False log = [] output_file = '' query_file = '' verbose = False opts = "ho:q:v" long_opts = ["help","output=","query=","verbose"] # ============================================================ # Capture argument list minus the program name. # ============================================================ args = sys.argv[1:] # ============================================================ # Use a try-except block. # ============================================================ try: # Assign the results of the getopt function. params, values = getopt.getopt(args, opts, long_opts) # Loop through the parameters. for curr_param, curr_value in params: if curr_param in ("-h","--help"): print(help()) elif curr_param in ("-o","--output"): output_file = curr_value elif curr_param in ("-q","--query"): query_file = curr_value elif curr_param in ("-v","--verbose"): verbose = True # Append entry to log. log.append('[' + curr_param + '][' + curr_value + ']') # Print verbose parameter handling. if verbose: print(" Parameter Diagnostics\n-------------------------") for i in log: print(i) # Exception block. except getopt.GetoptError as e: # output error, and return with an error code print (str(e))

You can run the program in Linux or Unix with the following syntax provided that you’ve already set the parameters to 755. That means granting the file owner with read, write, and execute privileges, and group and other with read and execute privileges.

./getopts.py -h -o output.txt -q query.sql -v

It would return the following:

 Program Help
+---------------+-------------+-------------------+
| -h  --help    |             | Help switch.      |
| -o  --output  | output_file | Output file name. |
| -q  --query   | query_file  | Query file name.  |
| -v  --verbose |             | Verbose switch.   |
+---------------+-------------+-------------------+
 
 Parameter Diagnostics
-------------------------
[-h][]
[-o][output.txt]
[-q][query.sql]
[-v][]

If you didn’t notice, I also took the opportunity to write the help display in such a way that a maintenance programmer could add another switch or parameter easily. This way the programmer only needs to add a new row of text and add an elif statement with the new switch or parameter.

I think using Python’s getopt library is the cleanest and simplest way to implement switch and parameter handling, after all it’s the basis for so many C derived libraries. However, if you must write your own, below is an approach that would work:

#!/usr/bin/python
 
# Import libraries.
import sys
import mysql.connector
from mysql.connector import errorcode
 
# ============================================================
#  Set local variables for switch and parameter placeholders.
# ============================================================
help = False
display = \
""" Program Help
+---------------+-------------+-------------------+
| -h  --help    |             | Help switch.      |
| -o  --output  | output_file | Output file name. |
| -q  --query   | query_file  | Query file name.  |
| -v  --verbose |             | Verbose switch.   |
+---------------+-------------+-------------------+"""
 
log = []
output = ''
query = ''
verbose = False
 
# ============================================================
#  Capture argument list minus the program name.
# ============================================================
args = sys.argv[1:]
 
# ============================================================
#  If one or more args exists and the first one is an
#  a string that can cast to an int, convert it to an int,
#  assign it to a variable, and ignore any other args
#  in the list.
# ============================================================
if len(args) > 1 and args[0].isdigit():
  powerIn = int(args[0])
 
# Check for switches and parameters.
if isinstance(args,list) and len(args) >= 1:
 
  # Set the limit of switches and parameters.
  argc = len(args)
 
  # Enumerate through switches first and then parameters.
  for i in range(argc):
    if args[i][0] == '-':
 
      # Evaluate switches and ignore any parameter value.
      if   args[i] in ['-h','--help']:
        help = True
 
        # Append entry to log.
        log.append('[' + str(args[i]) + ']')
 
      elif args[i] in ['-v','--verbose']:
        verbose = True
 
        # Append entry to log.
        log.append('[' + str(args[i]) + ']')
 
      # Evaluate parameters.
      elif i < argc and not args[i+1][0] == '-':
        if   args[i] in ['-q','--query']:
          query = args[i+1]
        elif args[i] in ['-o','--output']:
          output = args[i+1]
 
        # Append entry to log.
        log.append('[' + str(args[i]) + '][' + args[i+1] + ']')
    else:
      continue
    continue
 
  # Print the help display when 
  if help: print(display)
 
  # Print the parameter handling collected in the log variable.
  if verbose: 
    for i in log: print(i)

#!/usr/bin/python # Import libraries. import sys import mysql.connector from mysql.connector import errorcode # ============================================================ # Set local variables for switch and parameter placeholders. # ============================================================ help = False display = \ """ Program Help +---------------+-------------+-------------------+ | -h --help | | Help switch. | | -o --output | output_file | Output file name. | | -q --query | query_file | Query file name. | | -v --verbose | | Verbose switch. | +---------------+-------------+-------------------+""" log = [] output = '' query = '' verbose = False # ============================================================ # Capture argument list minus the program name. # ============================================================ args = sys.argv[1:] # ============================================================ # If one or more args exists and the first one is an # a string that can cast to an int, convert it to an int, # assign it to a variable, and ignore any other args # in the list. # ============================================================ if len(args) > 1 and args[0].isdigit(): powerIn = int(args[0]) # Check for switches and parameters. if isinstance(args,list) and len(args) >= 1: # Set the limit of switches and parameters. argc = len(args) # Enumerate through switches first and then parameters. for i in range(argc): if args[i][0] == '-': # Evaluate switches and ignore any parameter value. if args[i] in ['-h','--help']: help = True # Append entry to log. log.append('[' + str(args[i]) + ']') elif args[i] in ['-v','--verbose']: verbose = True # Append entry to log. log.append('[' + str(args[i]) + ']') # Evaluate parameters. elif i < argc and not args[i+1][0] == '-': if args[i] in ['-q','--query']: query = args[i+1] elif args[i] in ['-o','--output']: output = args[i+1] # Append entry to log. log.append('[' + str(args[i]) + '][' + args[i+1] + ']') else: continue continue # Print the help display when if help: print(display) # Print the parameter handling collected in the log variable. if verbose: for i in log: print(i)

As you can see from the example, I didn’t give it too much effort. I think it should prove you should use the approach adopted by the general Python community.

I promised to give my students a full example of how to write and execute a Python object. There were two motivations for this post. The first was driven by my students trying to understand the basics and the second my somebody else saying Python couldn’t deliver objects. Hopefully, this code is simple enough for both audiences. I gave them this other tutorial on writing and mimicking overloaded Python functions earlier.

This defines a Ball object type and a FilledBall object subtype of Ball. It incorporates the following elements:

A special __init__ function, which is a C/C++ equivalent to a constructor.
A special __str__ function represents a class object instance as a string. It is like the getString() equivalent in the Java programming language.
A bounce instance function, which means it acts on any instance of the Ball object type or FilledBall object subtype.
A get_direction instance function and it calls the __format local object function, which is intended to mimic a private function call, like other object-oriented programming languages.
A private name __format function (Private name mangling: When an identifier that textually occurs in a class definition begins with two or more underscore characters and does not end in two or more underscores, it is considered a private name of that class.)

You can test this code by creating the $PYTHONPATH (Unix or Linux) or %PYTHONPATH% (Windows) as follows with all the code inside the present working directory, like this in Unix or Linux:

export set $PYTHONPATH=.

Then, you create the Ball.py file with this syntax:

# Creates a Ball object type and FilledBall object subtype.
class Ball:
  # User-defined constructor with required parameters.
  def __init__(self, color = None, radius = None, direction = None):
    # Assign a default color value when the parameter is null.
    if color is None:
      self.color = "Blue"
    else:
      self.color = color.lower()
 
    # Assign a default radius value when the parameter is null.
    if radius is None:
      self.radius = 1
    else:
      self.radius = radius
 
    # Assign a default direction value when the parameter is null.
    if direction is None:
      self.direction = "down"
    else:
      self.direction = direction.lower()
 
    # Set direction switch values.
    self.directions = ("down","up")
 
  # User-defined standard function when printing an object type.
  def __str__(self):
    # Build a default descriptive message of the object.
    msg = "It's a " + self.color + " " + str(self.radius) + '"' + " ball"
 
    # Return the message variable.
    return msg
 
  # Define a bounce function.
  def bounce(self, direction = None):
    # Set direction on bounce.
    if not direction is None:
      self.direction = direction
    else:
      # Switch directions.
      if self.directions[0] == self.direction:
        self.direction = self.directions[1]
      elif self.directions[1] == self.direction:
        self.direction = self.directions[0]
 
  # Define a bounce function.
  def getDirection(self):
    # Return current direction of ball.
    return self.__format(self.direction)
 
  # User-defined pseudo-private function, which is available
  # to instances of the Ball object and any of its subtypes.
  def __format(self, msg):
    return "[" + msg + "]"
 
# This is the object subtype, which takes the parent class as an
# argument.
class FilledBall(Ball):
  def __init__(self, filler = None):
    # Instantiate the parent class and then any incremental 
    # parameter values.
    Ball.__init__(self,"Red",2)
 
    # Add a default value or the constructor filler value.
    if filler is None:
      self.filler = "Air".lower()
    else:
      self.filler = filler
 
  # User-defined standard function when printing an object type, which 
  # uses generalized invocation.
  def __str__(self):
    # Build a default descriptive message of the object.
    msg = Ball.__str__(self) + str(" filled with " + self.filler)
 
    # Return the message variable.
    return msg

# Creates a Ball object type and FilledBall object subtype. class Ball: # User-defined constructor with required parameters. def __init__(self, color = None, radius = None, direction = None): # Assign a default color value when the parameter is null. if color is None: self.color = "Blue" else: self.color = color.lower() # Assign a default radius value when the parameter is null. if radius is None: self.radius = 1 else: self.radius = radius # Assign a default direction value when the parameter is null. if direction is None: self.direction = "down" else: self.direction = direction.lower() # Set direction switch values. self.directions = ("down","up") # User-defined standard function when printing an object type. def __str__(self): # Build a default descriptive message of the object. msg = "It's a " + self.color + " " + str(self.radius) + '"' + " ball" # Return the message variable. return msg # Define a bounce function. def bounce(self, direction = None): # Set direction on bounce. if not direction is None: self.direction = direction else: # Switch directions. if self.directions[0] == self.direction: self.direction = self.directions[1] elif self.directions[1] == self.direction: self.direction = self.directions[0] # Define a bounce function. def getDirection(self): # Return current direction of ball. return self.__format(self.direction) # User-defined pseudo-private function, which is available # to instances of the Ball object and any of its subtypes. def __format(self, msg): return "[" + msg + "]" # This is the object subtype, which takes the parent class as an # argument. class FilledBall(Ball): def __init__(self, filler = None): # Instantiate the parent class and then any incremental # parameter values. Ball.__init__(self,"Red",2) # Add a default value or the constructor filler value. if filler is None: self.filler = "Air".lower() else: self.filler = filler # User-defined standard function when printing an object type, which # uses generalized invocation. def __str__(self): # Build a default descriptive message of the object. msg = Ball.__str__(self) + str(" filled with " + self.filler) # Return the message variable. return msg

Next, let’s test instantiating the Ball object type with the following code:

#!/usr/bin/python
 
# Import the Ball class into its own namespace.
import Ball
 
# Assign an instantiated class to a local variable.
myBall = Ball.Ball()
 
# Check whether the local variable holds a valid Ball instance.
if not myBall is None:
  print(myBall, "instance.")
else:
  print("No Ball instance.")
 
# Loop through 10 times changing bounce direction.
for i in range(1,10):
  # Find dirction of ball.
  print(myBall.getDirection())
 
  # Bounce the ball.
  myBall.bounce()

Next, let’s test instantiating the FilledBall object subtype with the following code:

#!/usr/bin/python
 
# Import the Ball class into its own namespace.
import Ball
 
# Assign an instantiated class to a local variable.
myBall = Ball.FilledBall()
 
# Check whether the local variable holds a valid FilledBall instance.
if not myBall is None:
  print(myBall, "instance.")
else:
  print("No Ball instance.")
 
# Loop through 10 times changing bounce direction.
for i in range(1,10):
  # Find dirction of ball.
  print(myBall.getDirection())
 
  # Bounce the ball.
  myBall.bounce()

As always, I hope this helps those looking to learn and extend their knowledge.

The following are samples of creating, changing, and removing users and groups in Linux. These are the command-line options in the event you don’t have access to the GUI tools.

Managing Users:

Adding a user:

The prototype is:

# useradd [-u uid] [-g initial_group] [-G group[,...]] \
 > [-d home_directory] [-s shell] [-c comment] \
 > [-m [-k skeleton_directory]] [-f inactive_time] \
 > [-e expire_date] -n username