How does Python handle repr for strings?

Question

I'm trying to emulate Python's repr exactly in Java; this includes the use of single quotes where possible. What method does Python use to determine what sort of quotes it should emit?

Edit: I'm looking for some actual code, somewhere in the web of Python. I've already looked at Objects/unicodeobject.c and some of Objects/strlib/, but I couldn't find anything besides escape sequences for Unicode.

On my terminal, the output by repr does not seem to change with respect to the type of quotes used to create the string. >>> repr("Hello") "'Hello'" >>> repr('Hello') "'Hello'" — smac89
– smac89, Commented Dec 13, 2014 at 23:25
@simonzack I have. I already extracted what I could from Objects/unicodeobject.c. — Octavia Togami
– Octavia Togami, Commented Dec 13, 2014 at 23:25
@Smac89 It doesn't store quote information, I got that much from the interpreter. — Octavia Togami
– Octavia Togami, Commented Dec 13, 2014 at 23:26
@Smac89 I'm looking to replicate the behavior of repr exactly in Java. This includes quotes. — Octavia Togami
– Octavia Togami, Commented Dec 13, 2014 at 23:27

f.rodrigues · Accepted Answer · 2014-12-13 23:21:38Z

1

I guess it will use single quotes unless it need to use it inside the string.

As show in:

print repr("Hello")
print repr('Hello')
print repr("Hell'o")
print repr('Hell"o')
print repr("""Hell'o Worl"o""")

Output:

'Hello'
'Hello'
"Hell'o" # only one using double quotes
'Hell"o'
'Hell\'o Worl"o' # handles the single quote with a \'

answered Dec 13, 2014 at 23:21

f.rodrigues

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2 Comments

Octavia Togami Over a year ago

I'm actually looking for an algorithm or similar from the source. I'll update the question.

simonzack Over a year ago

@ıɯɐƃoʇǝızuǝʞ IMO your question is clear enough, but some stackoverflow users do not read the question at all.

Octavia Togami · Accepted Answer · 2014-12-14 00:15:19Z

1

From what I could extract out of Objects/byteobject.c (here), this is the section that does it:

quote = '\'';
if (smartquotes && squotes && !dquotes)
    quote = '"';
if (squotes && quote == '\'') {
    if (newsize > PY_SSIZE_T_MAX - squotes)
        goto overflow;
    newsize += squotes;
}

So, if there is no double quotes and there is single quotes it uses double quotes, otherwise single quotes.

answered Dec 14, 2014 at 0:15

Octavia Togami

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1 Comment

demented hedgehog Over a year ago

Yeah.. I think it depends on whether you want the ascii strings or the unicode strings. There's a similar block of code in unicode_repr. And since strings are unicode by default in python3 it's more likely the unicode version is the one you want.

demented hedgehog · Accepted Answer · 2014-12-14 00:23:10Z

1

https://github.com/python/cpython/tree/master/Objects/unicodeobject.c

static PyObject *
unicode_repr(PyObject *unicode)
{ ...

unicode_repr in here github.com/python/cpython/blob/master/Objects/unicodeobject.c by the looks of it.

NOTE: I've updated this answer to remove out-of-date info and point to the current repo

edited Dec 14, 2014 at 0:23

answered Dec 13, 2014 at 23:53

demented hedgehog

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7 Comments

Octavia Togami Over a year ago

Additionally, latest 3.4 source, I should have said. Oh well, this extremely outdated git mirror will work too. I might be able to track down where stringobject.c disappeared to.

demented hedgehog Over a year ago

Get the source distro from python.org.

Octavia Togami Over a year ago

(for future reference the official mirror is here)

demented hedgehog Over a year ago

Hmm .. not immediately obvious.. PyObject_Repr is calling res = (*v->ob_type->tp_repr)(v); I can't see something that's obviously the unicode (or string) object type.

Octavia Togami Over a year ago

Also, I'm not a C person so this is half guess work on my part.

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