Archive for December, 2024
Using Python’s getopt
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. 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.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 | #!/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 = "" help = ((' Program Help') \ ,('+---------------+-------------+-------------------+') \ ,('| -h --help | | Help switch. |') \ ,('| -o --output | output_file | Output file name. |') \ ,('| -q --query | query_file | Query file name. |') \ ,('| -v --verbose | | Verbose switch. |') \ ,('+---------------+-------------+-------------------+')) # Translate list of tuples to a return delimited string. for i in help: display = display + i + "\n" # 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 tuple collection 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 tuple in the help tuple 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:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 | #!/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: for i in display: print(i) # 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.
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