PEP-515 (underscores in numeric literals) and .format width specifier

Python Help
1

Hello all,
I stumbled across this behavior and wondered if it was done for a reason. When trying out underscores in hex strings, I would have expected the underscore to NOT be included in the width of the numeric literal, but it is:

# 32-bit hex value, 0x0ee1_f00d
print('0x{:08X}'.format(0x0ee1_f00d))
# prints 0x0EE1F00D (0x plus 8 digits; great)
print('0x{:08_X}'.format(0x0ee1_f00d))
# prints 0xEE1_F00D (0x plus 7 digits plus _)
print('0x{:09_X}'.format(0x0ee1_f00d))
# prints 0x0EE1_F00D (0x plus 8 digits plus  _)

This problem is going to compound given that I also have to deal with 64-bit values, 48-bit values, 24-bit values, etc.

Thanks in advance for any help/explanations.

2

As the field width is often used for column alignment and formatting, I would think it odd to not include any character in the width. Rather than “how many digits should be printed?”, it’s “how wide should this field be in the output?”.

3

Underscores in numeric literals are irrelevant. There is no difference to Python whether you write 0x0ee1f00d or 0x0_e_e_1_f_0_0_d or 249688077, they are all the same number.

The format width field is the minimum width of the string, and it includes everything in the string: spaces, zeroes, decimal points (for floats), leading negative sign, everything. Why should underscores be different?

I don’t understand what “problem” you are experiencing.

What is the width you want the string to have? If it is eight hex digits plus an underscore, that makes 9 so your minimum width is 9. Where is the problem?

(Remember that if the string is larger than the minimum width, it will not be truncated.)

4

From string — Common string operations — Python 3.11.0 documentation
" width is a decimal integer defining the minimum total field width, including any prefixes, separators, and other formatting characters."

>>> print('0x{:8_X}'.format(0xeee1_f00d))
0xEEE1_F00D # 8 minimum, 9 needed