Programming Forums > Script Programming > Python

Dietrich · May 4th, 2005, 8:26 AM

It was al1986 who got me into this ...

The reversed() function returns an iterator object. Try invoking a next() method on this object. Alternatively, you can loop through the items by doing

(Toggle Plain Text)

for i in mysortedlist: print i

So I tried this ...

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x = [1,2,3,4]
print "original list =", x
rx = reversed(x)
for i in rx: print i,
print

Then this ...

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x = [1,2,3,4]
print "original list =", x
rx = reversed(x)
print "rx.next() =", rx.next()
print "rx.next() =", rx.next()
print "rx.next() =", rx.next()

When I combine the two codes I get an error that does not like next() or rx ...

(Toggle Plain Text)

x = [1,2,3,4]
print "original list =", x
rx = reversed(x)
for i in rx: print i,
print
print "rx.next() =", rx.next()
print "rx.next() =", rx.next()
print "rx.next() =", rx.next()

It acts like rx has been soiled, any idea what is going on?

hydroxide · May 4th, 2005, 7:36 PM

Quote:

Originally Posted by Dietrich

It acts like rx has been soiled, any idea what is going on?

When you do for i in rx..., you entirely consume the iterator. An iterator will raise a StopIteration when it has no more elements to yield:

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x = iter(range(4))
for i in x:
    print i
    if i%2:
        break
print "!!"
print x.next()
print x.next()
print x.next()  # <--Boom

--OH.

Dietrich · May 4th, 2005, 9:08 PM

Thanks hydroxide!

When I did a few print rx to check, the iterator seemed to be unchanged.

May 4th, 2005, 8:26 AM	#1
Dietrich Professional Programmer Join Date: Feb 2005 Posts: 434 Rep Power: 4	Using reversed and next It was al1986 who got me into this ... The reversed() function returns an iterator object. Try invoking a next() method on this object. Alternatively, you can loop through the items by doing (Toggle Plain Text) for i in mysortedlist: print i for i in mysortedlist: print i So I tried this ... (Toggle Plain Text) x = [1,2,3,4] print "original list =", x rx = reversed(x) for i in rx: print i, print x = [1,2,3,4] print "original list =", x rx = reversed(x) for i in rx: print i, print Then this ... (Toggle Plain Text) x = [1,2,3,4] print "original list =", x rx = reversed(x) print "rx.next() =", rx.next() print "rx.next() =", rx.next() print "rx.next() =", rx.next() x = [1,2,3,4] print "original list =", x rx = reversed(x) print "rx.next() =", rx.next() print "rx.next() =", rx.next() print "rx.next() =", rx.next() When I combine the two codes I get an error that does not like next() or rx ... (Toggle Plain Text) x = [1,2,3,4] print "original list =", x rx = reversed(x) for i in rx: print i, print print "rx.next() =", rx.next() print "rx.next() =", rx.next() print "rx.next() =", rx.next() x = [1,2,3,4] print "original list =", x rx = reversed(x) for i in rx: print i, print print "rx.next() =", rx.next() print "rx.next() =", rx.next() print "rx.next() =", rx.next() It acts like rx has been soiled, any idea what is going on? __________________ I looked it up on the Intergnats!

May 4th, 2005, 9:08 PM	#3
Dietrich Professional Programmer Join Date: Feb 2005 Posts: 434 Rep Power: 4	Thanks hydroxide! When I did a few print rx to check, the iterator seemed to be unchanged. __________________ I looked it up on the Intergnats!

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Programming Forums > Script Programming > Python

Using reversed and next