Using python to dump hexadecimals into YAML

Question

Now I'm dumping into a YAML document. It's working as it should for the most part. When I try to dump a hexadecimal such as "0x2A" it converts to 42. Isn't there any way to maintain it's hexadecimal format? A string won't work sadly. And int( 0x2A, 16) also just gives me a 42.

Answer 1

This should do it:

>>> import yaml
>>> class HexInt(int): pass
... 
>>> def representer(dumper, data):
...     return yaml.ScalarNode('tag:yaml.org,2002:int', hex(data))
... 
>>> yaml.add_representer(HexInt, representer)
>>> yaml.dump({"n": HexInt(42)})
'{n: 0x2a}\n'

Answer 2

You may be looking for hex(0x2a) == hex(42) == '0x2a'.

Unless you're looking for a way to convince your existing dumping function to use hexadecimal instead of decimal notation...

---

Answering to your comment below, if the problem is that you want upper case letters for the hexadecimal digits (but lower case for the 0x) then you have to use string formatting. You can choose one of the following:

"0x%02X" % 42                     # the old way
"0x{:02X}".format(42) == "0x2A"   # the new way

In both cases, you'll have to print the 0x explicitly, followed by a hexadecimal number of at least two digits in upper case, left-padded with a zero if your number has only one digit. This is denoted by the format 02X, same as in C's printf.

Answer 3

Representing all int in hex format, without a HexInt class, can be done using:

def hexint_presenter(dumper, data):
    return dumper.represent_int(hex(data))
yaml.add_representer(int, hexint_presenter)

With reference to this answer.