Python "del" syntax error when used as a variable name

Question

I am building a todo-list CLI and it requires a del argument for deleting an entry from the list. The CLI usage is as given below

$ ./todo help
Usage :-
$ ./todo add "todo item"  # Add a new todo
$ ./todo ls               # Show remaining todos
$ ./todo del NUMBER       # Delete a todo
$ ./todo done NUMBER      # Complete a todo
$ ./todo help             # Show usage
$ ./todo report           # Statistics

But in python( I am using python 3.8.3) when using the argparse module for parsing the arguments from command line the code for the above specified feature is as follows

parser.add_argument("--del", type=int, help="Delete a todo")

The problem arises since del is a reserved keyword by python for completely different purpose and so it gives a syntax error when reading that line of code

print (args.del)

syntax highlight image

Error message is as follows

File "todo.py", line 24
    if args.del:
            ^
SyntaxError: invalid syntax

syntax error image

Is there a solution to use del as per requirements of the project.

why not change `del` to `delete` as `del` is a reserved keyword — Vaebhav, Dec 31 '20 at 07:18
yeah i know that too but the moderators of the project asked to use "del" as a CLI argument, what is the possible solution to this. Check the usage described in the question body. — Sarath Sajan, Dec 31 '20 at 07:20
Here is the GitHub repo issue I made, if it helps in any way. https://github.com/nseadlc-2020/package-todo-cli-task/issues/51 — Sarath Sajan, Dec 31 '20 at 07:21
Use `dest=` to change the eventual name of the argument to a non-reserved keyword https://docs.python.org/3/library/argparse.html#dest — Iain Shelvington, Dec 31 '20 at 07:22

score 5 · Accepted Answer · answered Dec 31 '20 at 07:27

The dest parameter can be passed to argparse.add_argument to change the eventual attribute name that the argument will be bound to. You can use this to change "del" to a non-reserved keyword attribute name

parser.add_argument('--del', type=int, help='Delete a todo', dest='should_delete')

score 2 · Answer 2 · answered Dec 31 '20 at 07:18

2

del is a reserved keyword. It cannot be used as an attribute.

In this case, you can use a string to dynamically access this attribute, however:

getattr(args, "del")

However, it is probably better to change this name.

answered Dec 31 '20 at 07:18

juanpa.arrivillaga

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rfkortekaas · Answer 3 · 2021-01-01T07:49:32.653

2

As del is a reserved keyword it cannot be used. However you can use dest to create a custom attribute and not use the auto generated attribute.

parser = argparse.ArgumentParser()
parser.add_argument('--del', dest='delete')
parser.parse_args('--del XXX'.split())

Results in: Namespace(delete='XXX')

edited Jan 01 '21 at 07:49

answered Dec 31 '20 at 07:31

rfkortekaas

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Python "del" syntax error when used as a variable name

3 Answers3