[SS]: Python's alike range. The semantic should be exactly the same (and seems the more sensible for Tcl also).

 # range ?start? end ?step?
 #
 # Python's alike range function.
 # Returns the [start,end) integer range.
 #
 # Example:
 #
 # foreach x [range 0 10] y [range 20 0 -2] {
 #     puts "$x $y"
 # }
 proc range args {
     set l [llength $args]
     if {$l == 1} {
 	set start 0
 	set step 1
 	set end [lindex $args 0]
     } elseif {$l == 2} {
 	set step 1
 	foreach {start end} $args break
     } elseif {$l == 3} {
 	foreach {start end step} $args break
     } else {
 	error {wrong # of args: should be "range ?start? end ?step?"}
     }
     set result {}
     if {$start <= $end} {
 	for {set j $start} {$j < $end} {incr j $step} {
 	    lappend result $j
 	}
     } else {
 	for {set j $start} {$j > $end} {incr j $step} {
 	    lappend result $j
 	}
     }
     return $result
 }
----
See also [Integer range generator]