At Saturday 7/10/2006 02:15, MonkeeSage wrote:
On Oct 6, 8:23 pm, Gabriel Genellina <[EMAIL PROTECTED]> wrote:
> if 2 in [1,2,3]: print "Use the same (in) operator"
> elif 'E' in ('E','r','i','k'): print "Works for any sequence"
> elif 'o' in 'hello': print "Even strings"
This isn't really analogous is it? For "somedict.has_key(k)" or "k in
somedict", you don't need to know the value of somedict[k] ahead of
time. So you can avoid KeyError by asking if the key exists first
before trying to get the value.
The meaning comes from the most common usage. For a list, you want to
know if an object is contained in the list (not if an index is in
range!). For a dictionary, you usually want to know if it maps
anything to a given key (not if any key maps to that value!). These
are the most common operations, and that's why they have the simple
sintax "a in b". [BTW, usage of operator "in" as "key in dict" is
rather new to Python; has_key() were the only way to test for key
existence some time ago].
Wouldn't that be more like this for
lists (and other sequences):
def has_index(seq, index):
try:
seq[index]
return True
except IndexError:
return False
I've often wondered why there is no built-in method like that for
sequence objects.
Because it's not needed at all: valid sequence indexes are *exactly*
range(len(seq)). This is the basic point of being a sequence: when
indexes are not contiguous, in fact you have a mapping, not a sequence.
And also why not the equivalent of dict.get for other
sequences:
def get(seq, index, default=None):
if has_index(seq, index):
return seq[index]
else:
return default
Seems useful...
Sometimes, maybe... But since you can write it efficientely in a few
lines when needed, I don't see the need to put it into the core language.
--
Gabriel Genellina
Softlab SRL
__________________________________________________
Preguntá. Respondé. Descubrí.
Todo lo que querías saber, y lo que ni imaginabas,
está en Yahoo! Respuestas (Beta).
¡Probalo ya!
http://www.yahoo.com.ar/respuestas
--
http://mail.python.org/mailman/listinfo/python-list
