Decorating Hex function to pad zeros

Question

I wrote this simple function:

def padded_hex(i, l):
    given_int = i
    given_len = l

    hex_result = hex(given_int)[2:] # remove '0x' from beginning of str
    num_hex_chars = len(hex_result)
    extra_zeros = '0' * (given_len - num_hex_chars) # may not get used..

    return ('0x' + hex_result if num_hex_chars == given_len else
            '?' * given_len if num_hex_chars > given_len else
            '0x' + extra_zeros + hex_result if num_hex_chars < given_len else
            None)

Examples:

padded_hex(42,4) # result '0x002a'
hex(15) # result '0xf'
padded_hex(15,1) # result '0xf'

Whilst this is clear enough for me and fits my use case (a simple test tool for a simple printer) I can't help thinking there's a lot of room for improvement and this could be squashed down to something very concise.

What other approaches are there to this problem?

Tim Pietzcker · Accepted Answer · 2018-03-08T15:48:17.850

201

Use the new .format() string method:

>>> "{0:#0{1}x}".format(42,6)
'0x002a'

Explanation:

{   # Format identifier
0:  # first parameter
#   # use "0x" prefix
0   # fill with zeroes
{1} # to a length of n characters (including 0x), defined by the second parameter
x   # hexadecimal number, using lowercase letters for a-f
}   # End of format identifier

If you want the letter hex digits uppercase but the prefix with a lowercase 'x', you'll need a slight workaround:

>>> '0x{0:0{1}X}'.format(42,4)
'0x002A'

Starting with Python 3.6, you can also do this:

>>> value = 42
>>> padding = 6
>>> f"{value:#0{padding}x}"
'0x002a'

edited Mar 08 '18 at 15:48

answered Sep 28 '12 at 10:43

Tim Pietzcker

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Is it possible to write this as a format string in python 3.6? – Richard Neumann Mar 08 '18 at 09:36
Yes, but without any success, since I cannot figure out the correct syntax for it: `value = 42; padding = 6; f"{value:#0{padding}x}"` throws a syntax error: ` File "", line 1 f"{value:#0{padding}x}" ^ SyntaxError: invalid syntax` – Richard Neumann Mar 08 '18 at 15:29
This works for me on Python 3.6.4. Try `import sys; print(sys.version)` to make sure you're running the correct interpreter. – Tim Pietzcker Mar 08 '18 at 15:45
python really likes to complicate things up – user7082181 Mar 22 '21 at 19:46

score 29 · Answer 2 · answered Sep 28 '12 at 10:40

29

How about this:

print '0x%04x' % 42

answered Sep 28 '12 at 10:40

georg

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use the `*` to pass width: `'0x%0*x' % (4,42) ` – Ashwini Chaudhary Sep 28 '12 at 10:49

score 10 · Answer 3 · answered Nov 03 '18 at 07:58

10

If just for leading zeros, you can try zfill function.

'0x' + hex(42)[2:].zfill(4) #'0x002a'

answered Nov 03 '18 at 07:58

Xinyi Li

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score 7 · Answer 4 · edited May 23 '17 at 12:17

7

Use * to pass width and X for uppercase

print '0x%0*X' % (4,42) # '0x002A'

As suggested by georg and Ashwini Chaudhary

edited May 23 '17 at 12:17

Community

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answered Aug 23 '14 at 23:41

GabrielOshiro

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What is the reason to use * to pass width? – tartaruga_casco_mole Oct 19 '16 at 17:44
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@RafaelJ To make it generic, instead of having it hardcoded – GabrielOshiro Oct 19 '16 at 19:01

Boris · Answer 5 · 2020-12-01T16:55:01.043

7

What I needed was

"{:02x}".format(7)   # '07'
"{:02x}".format(27)  # '1b'

Where : is the start of the formatting specification for the first argument {} to .format(), then 02 means "pad the input from the left with 0s to length 2" and x means "format as hex with lowercase letters".

The above can also be done with f-strings:

f"{7:02x}"   # '07'
f"{27:02x}"  # '1b'

edited Dec 01 '20 at 16:55

answered Jan 01 '20 at 13:07

Boris

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score 1 · Answer 6 · answered Mar 10 '19 at 16:19

1

Suppose you want to have leading zeros for hexadecimal number, for example you want 7 digit where your hexadecimal number should be written on, you can do like that :

hexnum = 0xfff
str_hex =  hex(hexnum).rstrip("L").lstrip("0x") or "0"
'0'* (7 - len(str_hexnum)) + str_hexnum

This gives as a result :

'0000fff'

answered Mar 10 '19 at 16:19

SENHAJI RHAZI Hamza

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`'%0*x' % (7,0xfff)` – jon Mar 11 '19 at 22:15

Decorating Hex function to pad zeros

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