Comma format

I discovered a shorthand I'm shocked I never knew before: f"{my_num:,}" will format 1234567 as 1,234,567. I knew about several other fstring numerical formats (I wrote the fstring answer for How to display a float with two decimal places?), but I never came across this one before. It looks odd at first, but it makes sense.

I also tried f"{1234567: } and which provides a leading space. Now, that would imply more than one space could work, but no, that's a ValueError. Apparently the feature is so you can align negatives:

>>> print(f"{1234567: }\n{-1234567: }")
 1234567
-1234567

In addition to , _ works too.

>>> print(f"{1234567:_}\n{-1234567:_}")
 1_234_567
-1_234_567

Which I suppose makes sense given python accepts _ in numbers for readability:

>>> a = 1_234_567
>>> a
1234567