Sometimes I find myself simply wanting the length of an iterator. For
example, to collect some (somewhat useless ;)) statistics about a program
of mine, I've got code like this:
objs = gc.get_objects( )
classes = len([obj for obj in objs if inspect.isclass (obj)])
functions = len([obj for obj in objs if inspect.isrouti ne(obj)])
modules = len([obj for obj in objs if inspect.ismodul e(obj)])
dicts = len([obj for obj in objs if type(obj) == types.DictType])
lists = len([obj for obj in objs if type(obj) == types.ListType])
tuples = len([obj for obj in objs if type(obj) == types.TupleType])
Now, obviously I can (and will, now that 2.3 is officially released :))
replace the list comprehensions with itertools.ifilt er, but I need an
itertools.ilen to find the length of such iterators.
I can imagine such a need arises in more useful situations than this, but
this is the particular case that brought the need to mind.
The Python code is simple, obviously:
def ilen(iterator):
i = 0
for _ in iterator:
i += 1
return i
But it's a pity to use itertools' super-fast iterators and have to use slow,
raw Python to determine their length :)
Jeremy 10 3392
"Jeremy Fincher" <fi*******@osu. edu> wrote in message
news:bg******** **@news.cis.ohi o-state.edu... Sometimes I find myself simply wanting the length of an iterator.
An iterator is a function/method that traverses (or possibly
generates) a seqeuence. The sequence has a length (actual or
potential) but the iterator does not.
For example, to collect some (somewhat useless ;)) statistics about a program of mine, I've got code like this:
objs = gc.get_objects( ) classes = len([obj for obj in objs if inspect.isclass (obj)]) functions = len([obj for obj in objs if
inspect.isrouti ne(obj)]) modules = len([obj for obj in objs if
inspect.ismodul e(obj)]) dicts = len([obj for obj in objs if type(obj) ==
types.DictType]) lists = len([obj for obj in objs if type(obj) ==
types.ListType]) tuples = len([obj for obj in objs if type(obj) ==
types.TupleType])
Alternative: initialize six counters to 0. Scan list once and update
appropriate counter.
Now, obviously I can (and will, now that 2.3 is officially released
:)) replace the list comprehensions with itertools.ifilt er, but I need
an itertools.ilen to find the length of such iterators.
You mean the associated sequence.
I can imagine such a need arises in more useful situations than
this, but this is the particular case that brought the need to mind.
The Python code is simple, obviously:
def ilen(iterator): i = 0 for _ in iterator: i += 1 return i
But it's a pity to use itertools' super-fast iterators and have to
use slow, raw Python to determine their length :)
If you mean a c-coded counter (which would not be an iterator itself)
equivalent to the above, that could be done. Perhaps len() could be
upgraded/extended to accept an iterator and count when it can't get a
__len__ method to call. The main downside is that iterators are
sometimes destructive (run once only).
In the meanwhile, is this really a bottleneck for you? or merely the
'pity' of a program running in 1 sec when 0.1 is possible?
Terry J. Reedy
"Terry Reedy" <tj*****@udel.e du> schrieb im Newsbeitrag
news:tp******** ************@co mcast.com... "Jeremy Fincher" <fi*******@osu. edu> wrote in message news:bg******** **@news.cis.ohi o-state.edu... Sometimes I find myself simply wanting the length of an iterator.
An iterator is a function/method that traverses (or possibly generates) a seqeuence. The sequence has a length (actual or potential) but the iterator does not.
Very well explained. There are lots of usefull generators with unlimited
sequences.
- random generators
- def achilles():
while 1
:N=1.
yield N
n=n/2
- def schoenberg():
cycle=range(12)
while 1:
shuffle(cycle)
for i in cycle:
yield i
There is no way to determined, whether such generartors will come to an
end - The Halting Problem for Turing Machines ;-)
Thus there will never be a safe len(iterator).
Kindly
Michael
Terry Reedy wrote: An iterator is a function/method that traverses (or possibly generates) a seqeuence. The sequence has a length (actual or potential) but the iterator does not.
Even some sequences don't have a length; consider (Lisp terminology)
"improper lists," where the cdr points to a cell earlier in the list. Or
any class with a somehow non-terminating __len__.
Alternative: initialize six counters to 0. Scan list once and update appropriate counter.
Yes, that works in this particular case, and is probably a superior
solution.
If you mean a c-coded counter (which would not be an iterator itself) equivalent to the above, that could be done. Perhaps len() could be upgraded/extended to accept an iterator and count when it can't get a __len__ method to call. The main downside is that iterators are sometimes destructive (run once only).
That's why I don't think such a change should be made to len(); *all*
iterators are destructive and len() silently destroying them doesn't seem
generally useful enough for the potential for mistake.
In the meanwhile, is this really a bottleneck for you? or merely the 'pity' of a program running in 1 sec when 0.1 is possible?
The whole of itertools really seems to exist because of the "pity" of taking
efficient iterators and turning them into lists in order to do any
significant manipulation of them. In that case, I would imagine the pity
of having to turn an interator into a sequence in order to determine the
length of the underlying sequence would be reason enough.
Jeremy
Michael Peuser wrote: There is no way to determined, whether such generartors will come to an end - The Halting Problem for Turing Machines ;-) Thus there will never be a safe len(iterator).
But then, there's no way to determine whether any given class' __len__ will
terminate, so you've got the same problem with len.
Granted, it's more likely to manifest itself with iterators and ilen than
with sequences and len, but if it's really an issue, ilen could take an
optional "max" argument for declaring a counter ilen isn't to exceed.
Jeremy
Another solution could be to implement custom lenght methods. However I see
no graceful way to do it with the quite tricky implementation (yield is the
only hint!) of 2.3.
It would be definitly easy with 2.2 "by hand" function factories (def
iter(), def __next__()), just def len() in addition and find the fastest
implementation
Kindly
Michael
"Jeremy Fincher" <fi*******@osu. edu> schrieb im Newsbeitrag
news:bg******** **@news.cis.ohi o-state.edu... Michael Peuser wrote: There is no way to determined, whether such generartors will come to an end - The Halting Problem for Turing Machines ;-) Thus there will never be a safe len(iterator). But then, there's no way to determine whether any given class' __len__
will terminate, so you've got the same problem with len.
Granted, it's more likely to manifest itself with iterators and ilen than with sequences and len, but if it's really an issue, ilen could take an optional "max" argument for declaring a counter ilen isn't to exceed.
Jeremy
"Jeremy Fincher" Sometimes I find myself simply wanting the length of an iterator. For example, to collect some (somewhat useless ;)) statistics about a program of mine, I've got code like this:
objs = gc.get_objects( ) classes = len([obj for obj in objs if inspect.isclass (obj)]) functions = len([obj for obj in objs if inspect.isrouti ne(obj)]) modules = len([obj for obj in objs if inspect.ismodul e(obj)]) dicts = len([obj for obj in objs if type(obj) == types.DictType]) lists = len([obj for obj in objs if type(obj) == types.ListType]) tuples = len([obj for obj in objs if type(obj) == types.TupleType])
Now, obviously I can (and will, now that 2.3 is officially released :)) replace the list comprehensions with itertools.ifilt er, but I need an itertools.ilen to find the length of such iterators.
I can imagine such a need arises in more useful situations than this, but this is the particular case that brought the need to mind.
The Python code is simple, obviously:
def ilen(iterator): i = 0 for _ in iterator: i += 1 return i
But it's a pity to use itertools' super-fast iterators and have to use slow, raw Python to determine their length :)
For your application, it is not hard to build a itertools version: import itertools def countif(predica te, seqn):
.... return sum(itertools.i map(predicate, seqn))
def isEven(x):
.... return x&1 == 0
countif(isEven, xrange(1000000) )
500000
def isTuple(x):
.... return type(x) == types.TupleType
tuples = countif(isTuple , objs)
Raymond Hettinger
On Thu, 07 Aug 2003 03:10:10 -0400, rumours say that Jeremy Fincher
<fi*******@osu. edu> might have written: objs = gc.get_objects( ) classes = len([obj for obj in objs if inspect.isclass (obj)]) functions = len([obj for obj in objs if inspect.isrouti ne(obj)]) modules = len([obj for obj in objs if inspect.ismodul e(obj)]) dicts = len([obj for obj in objs if type(obj) == types.DictType]) lists = len([obj for obj in objs if type(obj) == types.ListType]) tuples = len([obj for obj in objs if type(obj) == types.TupleType])
Another way to count objects:
# code start
import types, gc
type2key = {
types.ClassType : "classes",
types.FunctionT ype: "functions" ,
types.MethodTyp e: "functions" ,
types.ModuleTyp e: "modules",
types.DictType: "dicts",
types.ListType: "lists",
types.TupleType : "tuples"
}
sums = {
"classes": 0, "functions" : 0, "modules": 0, "dicts": 0,
"lists": 0, "tuples": 0
}
for obj in gc.get_objects( ):
try:
sums[type2key[type(obj)]] += 1
except KeyError:
pass
# code end
This code is intended to be <2.3 compatible.
--
TZOTZIOY, I speak England very best,
Microsoft Security Alert: the Matrix began as open source.
Christos "TZOTZIOY" Georgiou <tz**@sil-tec.gr> wrote in
news:98******** *************** *********@4ax.c om: Another way to count objects:
# code start import types, gc
type2key = { types.ClassType : "classes", types.FunctionT ype: "functions" , types.MethodTyp e: "functions" , types.ModuleTyp e: "modules", types.DictType: "dicts", types.ListType: "lists", types.TupleType : "tuples" }
sums = { "classes": 0, "functions" : 0, "modules": 0, "dicts": 0, "lists": 0, "tuples": 0 }
for obj in gc.get_objects( ): try: sums[type2key[type(obj)]] += 1 except KeyError: pass # code end
I'm just curious, why did you decide to map the types to strings instead of
just using the types themselves?
e.g. import gc sums = {} for obj in gc.get_objects( ):
if type(obj) not in sums:
sums[type(obj)] = 1
else:
sums[type(obj)] += 1
for typ, count in sums.iteritems( ):
print typ.__name__, count
instance 525
tuple 4273
class 162
getset_descript or 14
traceback 2
wrapper_descrip tor 165
list 258
module 71
instance method 279
function 1222
weakref 18
dict 1647
method_descript or 82
member_descript or 75
frame 18
--
Duncan Booth du****@rcp.co.u k
int month(char *p){return(1248 64/((p[0]+p[1]-p[2]&0x1f)+1)%12 )["\5\x8\3"
"\6\7\xb\1\x9\x a\2\0\4"];} // Who said my code was obscure?
Duncan Booth wrote: I'm just curious, why did you decide to map the types to strings instead of just using the types themselves?
So I can pluralize them in my output.
Jeremy This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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