Flag with default value as TRUE

[mansunkuo]

Hi, I found that the add_argument function doesn't work with default value as TRUE.

An minimum example flag_error.R is attached. It looks like:

#!/usr/bin/env Rscript
library(argparser, quietly = TRUE)
p <- arg_parser("Hi!")
p <- add_argument(p, arg = "--flag", short = "-f", flag = TRUE, default = TRUE, help = "a flag")
args <- parse_args(p)
print(args)

Without -f:

 ./flag_error.R

1 [1] FALSE

$help [1] FALSE

$flag [1] TRUE

$opts [1] NA

With -f:

./flag_error.R -f

Error in preprocess_argv(argv, parser) :

Insufficient number of arguments supplied for --flag

Calls: parse_args -> preprocess_argv

Execution halted

Is there any way to set a flag with default value as TRUE?

[David Shih]

As mentioned in ?add_argument, flags do not consume a value.

Flags are always in the off (FALSE) state by default. This is the common behaviour of most Linux programs.

If you really want to use a Boolean option, don't set the option as a flag. Just specify a default value of TRUE or FALSE.

Beware that the definition of TRUE and FALSE vary among programming/scripting languages, and some users may expect 1 to be converted to TRUE and 0 to be converted to FALSE. This is not the case in R.

library(argparser, quietly=TRUE);

pr <- arg_parser("Test binary")
pr <- add_argument(pr, "--binary", default = TRUE, help = "a binary option")

parse_args(pr);

parse_args(pr, c("-b", "FALSE"));  # FALSE

parse_args(pr, c("-b", "False"));  # FALSE

parse_args(pr, c("-b", "false"));  # FALSE

parse_args(pr, c("-b", "F"));  # FALSE

parse_args(pr, c("-b", "f"));  # NA

parse_args(pr, c("-b", "0"));  # NA

parse_args(pr, c("-b", "TRUE"));  # TRUE

parse_args(pr, c("-b", "True"));  # TRUE

parse_args(pr, c("-b", "true"));  # TRUE

parse_args(pr, c("-b", "T"));  # TRUE

parse_args(pr, c("-b", "t"));  # NA

parse_args(pr, c("-b", "1"));  # NA

[David Shih]

Not a bug.

[Mansun Kuo]

Hi David,

Thanks for your explanation!!! This library save me a lot of time.

In Python, it is possible to add an argument with action = store_true or store_false to adjust the default value of a logical argument. But I think your point of view is also good and reasonable.
Thanks for your great work!

Sincerely,
Mansun

[David Shih]

The similarity of argparser to Python's argparse has caused some confusion. I added some clarification to ?add_argument in the latest commit. I'll add some examples at some point.