Good point, Andrew!
I missed including the unit tests I wrote. I will now, at the bottom.
For reference, this is the implementation of *findall()*:
static PyObject *
_sre_SRE_Pattern_findall_impl(PatternObject *self, PyObject *string,
Py_ssize_t pos, Py_ssize_t endpos)
/*[clinic end generated code: output=f4966baceea60aca
input=5b6a4ee799741563]*/
{
SRE_STATE state;
PyObject* list;
Py_ssize_t status;
Py_ssize_t i, b, e;
if (!state_init(&state, self, string, pos, endpos))
return NULL;
list = PyList_New(0);
if (!list) {
state_fini(&state);
return NULL;
}
while (state.start <= state.end) {
PyObject* item;
state_reset(&state);
state.ptr = state.start;
status = sre_search(&state, PatternObject_GetCode(self));
if (PyErr_Occurred())
goto error;
if (status <= 0) {
if (status == 0)
break;
pattern_error(status);
goto error;
}
/* don't bother to build a match object */
switch (self->groups) {
case 0:
b = STATE_OFFSET(&state, state.start);
e = STATE_OFFSET(&state, state.ptr);
item = getslice(state.isbytes, state.beginning,
string, b, e);
if (!item)
goto error;
break;
case 1:
item = state_getslice(&state, 1, string, 1);
if (!item)
goto error;
break;
default:
item = PyTuple_New(self->groups);
if (!item)
goto error;
for (i = 0; i < self->groups; i++) {
PyObject* o = state_getslice(&state, i+1, string, 1);
if (!o) {
Py_DECREF(item);
goto error;
}
PyTuple_SET_ITEM(item, i, o);
}
break;
}
status = PyList_Append(list, item);
Py_DECREF(item);
if (status < 0)
goto error;
state.must_advance = (state.ptr == state.start);
state.start = state.ptr;
}
state_fini(&state);
return list;
error:
Py_DECREF(list);
state_fini(&state);
return NULL;
}
As far as I understand it, my implementation of *findalliter()* matches the
semantics in the *switch* statement.
This is my unit test. As you noted, it's not complete as it lacks a case
for unmatched groups.
def test_findfirst():
def check(pattern, string):
try:
g = re.findall(pattern, string)
assert findfirst(pattern, string) == g[0], '%s %s' % (pattern,
string)
assert list(findalliter(pattern, string)) == g, '%s %s' %
(pattern, string)
except ValueError:
assert len(g) == 0
with pytest.raises(ValueError):
findfirst(pattern, string)
s = 'xxxaxxxxbxxx'
check('a', s)
check('(a)', s)
check('(a|b)', s)
check('a.*b', s)
check('(a).*(b)', s)
# no match
check('y', s)
assert findfirst('y', s, default='THE DEFAULT') == 'THE DEFAULT'
base = s
for i in range(2, 10):
s = base * i
g = re.findall('a', s)
assert len(g) > 1
check('a', s)
check('(a)', s)
check('(a|b)', s)
check('a.*b', s)
check('(a).*(b)', s)
check('y', s)
You're right about *findall()* *always* returning srings:
[ins] In [1]: import re
[ins] In [2]: re.findall(r'(a).*(b)?.*(c)', 'axxxxxxxxxxxxc')
Out[2]: [('a', '', 'c')]
[ins] In [3]:
This is the matching implementation:
for m in re.finditer(pattern, string, flags=flags):
g = m.groups()
if len(g) == 1:
yield g[0]
elif g:
yield tuple(s if s else '' for s in g)
else:
yield m.group()
Updated unit test:
def test_findfirst():
def check(pattern, string):
try:
g = re.findall(pattern, string)
assert findfirst(pattern, string) == g[0], '%s %s' % (pattern,
string)
assert list(findalliter(pattern, string)) == g, '%s %s' %
(pattern, string)
except ValueError:
assert len(g) == 0
with pytest.raises(ValueError):
findfirst(pattern, string)
def all_checks(s):
check('a', s)
check('(a)', s)
check('(a|b)', s)
check('a.*b', s)
check('(a).*(b)', s)
check('(a).*(c)?.*(b)', s) # non-matching group
# no match
check('y', s)
check('(y)?.*(z)?.*(q)', s)
# empty matches
check('(a).*(y?).*(b)', s)
assert findfirst('y', s, default='THE DEFAULT') == 'THE DEFAULT'
s = 'xxxaxxxxbxxx'
all_checks(s)
base = s
for i in range(2, 10):
s = base * i
g = re.findall('a', s)
assert len(g) == i
all_checks(s)
Cheers,
On Fri, Dec 27, 2019 at 5:37 PM Andrew Barnert <abarn...@yahoo.com> wrote:
> > On Dec 27, 2019, at 09:00, Juancarlo Añez <apal...@gmail.com> wrote:
> >
> > for m in re.finditer(pattern, string, flags=flags):
> > g = m.groups()
> > if len(g) == 1:
> > yield g[0]
> > elif g:
> > yield g
> > else:
> > yield m.group()
>
> I don’t think this does the same thing as findall in every case. For
> example, for capture groups that don’t participate in the match, you’ll get
> tuples like ('spam', None, '42'), when I’m pretty sure findall always has
> strings no matter what. I’m not sure exactly what the rule is for how it
> does that: maybe it’s just the same thing as m.groups(default='') would
> give you?
>
> At any rate, it seems like this isn’t as trivial to port from C as it
> looked, so this needs solid unit tests. (Maybe the ones for findall are
> already good enough if you just adapt them?)
>
> That’s also a great argument that it should be added to the re module, so
> people don’t have to try to figure out how to port C code to Python and
> then test the hell out of it just to get something that’s only missing in
> the first place for historical/naming reasons.
>
>
>
--
Juancarlo *Añez*
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