Get str repr with double quotes Python

Question

I'm using a small Python script to generate some binary data that will be used in a C header.

This data should be declared as a char[], and it will be nice if it could be encoded as a string (with the pertinent escape sequences when they are not in the range of ASCII printable chars) to keep the header more compact than with a decimal or hexadecimal array encoding.

The problem is that when I print the repr of a Python string, it is delimited by single quotes, and C doesn't like that. The naive solution is to do:

'"%s"'%repr(data)[1:-1]

but that doesn't work when one of the bytes in the data happens to be a double quote, so I'd need them to be escaped too.

I think a simple replace('"', '\\"') could do the job, but maybe there's a better, more pythonic solution out there.

Extra point:

It would be convenient too to split the data in lines of approximately 80 characters, but again the simple approach of splitting the source string in chunks of size 80 won't work, as each non printable character takes 2 or 3 characters in the escape sequence. Splitting the list in chunks of 80 after getting the repr won't help either, as it could divide escape sequence.

Any suggestions?

Answer 1

You could try json.dumps:

>>> import json
>>> print(json.dumps("hello world"))
"hello world"

>>> print(json.dumps('hëllo "world"!'))
"h\u00ebllo \"world\"!"

I don't know for sure whether json strings are compatible with C but at least they have a pretty large common subset and are guaranteed to be compatible with javascript;).

Answer 2

Better not hack the repr() but use the right encoding from the beginning. You can get the repr's encoding directly with the encoding string_escape

>>> "naïveté".encode("string_escape")
'na\\xc3\\xafvet\\xc3\\xa9'
>>> print _
na\xc3\xafvet\xc3\xa9

For escaping the "-quotes I think using a simple replace after escape-encoding the string is a completely unambiguous process:

>>> '"%s"' % 'data:\x00\x01 "like this"'.encode("string_escape").replace('"', r'\"')
'"data:\\x00\\x01 \\"like this\\""'
>>> print _
"data:\x00\x01 \"like this\""