take defaults and types from keyword arguments

[tmbdev]

Consider the following little program:

import click                                                                    
                                                                                
@click.command()                                                                
#@click.option("--arg")  #(1)                                                       
@click.option("--arg", default=17)  #(2)
def command(arg=19):                                                            
    print(arg, type(arg))                                                       
                                                                                
if __name__=='__main__':                                                        
    command()   

Here, if using declaration (1), passing an argument with --arg will result in the passing of a string argument. On the other hand, declaration (2) overrides the default and forces the programmer to repeat defaults.

It would seem to be nicer behavior if @click.option used reflection to get the default value from keyword arguments, removing the need for duplication of the default and avoiding potential type inconsistencies.

(Perhaps to avoid backwards incompatibility where people rely on the odd current behavior, the fix could use a slight variant, say, @click.opt. When used with default=, it would just behave as the current options.)

import click                                                                    
                                                                                
@click.command()
@click.opt("--arg", help="defaults to '19' of type 'int'")
def command(arg=19):
    print(arg, type(arg))
     
if __name__=='__main__':
    command()

[davidism]

Thanks for the suggestion. This is essentially a duplicate of #1456, replacing introspecting annotations with introspecting defaults. We don't plan to add this at this time.

[tmbdev]

#1456 suggests using Python3-specific type annotations. I'm suggesting something much simpler: when no "default=" argument is given to @click.option, just use the default value from the argspec and continue as before:

    # inside @click.option
    if default is None:
        sig = inspect.signature(f)
        if option_name in sig:
            default = sig.parameters.[option_name].value
    # continue as before