I've found a bug with argparse and reported it upstream.
`command --option source destination` works
`command soucre destination --option` works
but `command source --option destination` doesn't outputting the usage text block associated `do_command` method and outputs error message `command: error: unrecognized arguments: destination`

This is when running is a shell which inherits from cmd.Cmd

The “cmd” module doesn’t use “argparse” as far as I can see. You might have to provide more information or code for someone to make sense of or reproduce your bug.

Also, see Issue 14191 which added new “parse_[known]_intermixed_args” APIs in 3.7, and have a look at Issue 15112, about intermixing options between particular kinds of positional parameters.

I've just done a test and from a command shell (bash or whatever) the following python script when ran produces the following

$ python3 command.py 0ne thwo three
files:  ['0ne', 'thwo', 'three']
sensors 1
freq 1200

$ python3 command.py -s 5 0ne thwo three
files:  ['0ne', 'thwo', 'three']
sensors 5
freq 1200

$ python3 command.py  0ne -s 5 thwo three
usage: command.py [-h] [-s SENSORS] [-f FREQ] file [file ...]
command.py: error: unrecognized arguments: thwo three

i've attached the program command.py

This is intended behavior of multi-nargs positionals.  The 'one' string is consumed by the 'file' argument, and there's no positional argument left to consume the other strings.  

The topic was raised and discussed previously  

https://bugs.python.org/issue14191 -argparse doesn't allow optionals within positionals

The fix is to use 'parser.parse_intermixed_args()', as documented in

https://docs.python.org/3/library/argparse.html#intermixed-parsing