The grouping string specifies the number of digits to group, going from right to left.
For example, the grouping: 321 means that the number 12345789 would be printed as in:
1,2,3,4,56,789
The above grouping string can be specified as:
grouping = 321
A grouping string of "0" or "" means: don't group. The default grouping string is "3".