It is a common practice to separate hex digits with a "thousands" separator every 4 hex digits.

0x1234_abcd

Although python does not accept the _ as a thousands separator in hex notation, neither is the thousands separator in base 10


Snippet that prints hex thousands with a _ separator

number = 0xef5678abcd1234

def hex_thousands(number):
    txt="{0:X}".format(number)
    txt_out = ""
    i = range(-4,-1 * (len(txt) + 4), -4)
    ii = i[:]
    ii.insert(0, None)
    for (j, k) in zip(i, ii):
        if txt_out:
            txt_out = "_" + txt_out
        txt_out = txt[j:k] + txt_out
    return txt_out

print hex_thousands(number)

How common is this 'common practice'?  Could you point to some publicly available examples? Are there other languages that have built-in facilities for dealing with hexadecimal representations of integers in this way?

I think I've seen hex strings separated by spaces every four digits, and by spaces or colons every two digits (though the latter was usually used for something that's better seen as a sequence of bytes rather than a hexadecimal representation of a large integer).  I've rarely seen the underscore separation that you describe, but perhaps that's because I haven't been looking in the right places.

Do you have a concrete proposal for amending the formatting mini-language syntax to support this?  Perhaps you could run this past the python-ideas mailing list to try to get support and to thrash out the details of a possible specification?

To me this seems to be adding yet more complication to an already complicated formatting mini-language for something that few people will ever need, so I'd be -1 on this as it stands.

Closing this for now;  if you want to pursue this, please take the suggestion to the python-ideas mailing list.

I'll work on a proposal for the ideas list.

Other language examples to keep this in a thread though.

perl -e 'print 0x1234_abcd; print "\n";'

C/C++ seems to not support the underscore.
Lua unsupported.

Data sheets from micro controllers and other digital circuits.

Bottom of page 21 on http://www.atmel.com/dyn/resources/prod_documents/32058S.pdf

I'm confused:  are you talking about producing underscores when formatting an integer for hexadecimal output, or allowing numeric literals to contain underscores?

Your perl example produces:

305441741

with not an underscore in sight.  I'm failing to understand the relevance of this example to your request.

Sorry my request is for output,  I am not requesting input.  The examples were for showing the use in other contexts of using an underscore as a word (4 hex digits) seperaror.

My assertions are from another area aside from computer languages,  but from documentation for components.  So I showed a documentation example and software examples that used or would not accept underscores.

the common pratice of using a space is not good for computer output to be used for parsing in following applications.