Get number of iteration

[Florian Lindner]

Hi!
If I iterate through a list, is there a way I can get the number of the
iteration: first, second, third, ...

l = ["three", "four", "five", "six"]
for x in l
print x
print x.iteration() # <- That's what I'm looking for!
print "next"

prints that:

three
1
next
four
2
next
fixe
3
next
six
4
next

Thx,
Florian

[Diez B. Roggisch]

Re: Get number of iteration

> If I iterate through a list, is there a way I can get the number of the[color=blue]
> iteration: first, second, third, ...
>
> l = ["three", "four", "five", "six"]
> for x in l
> print x
> print x.iteration() # <- That's what I'm looking for!
> print "next"[/color]

No, this won't work - x is the value of the list element, not an c++-like
iterator-object (that has to be dereferenced before accessing the actual
value).

So usually x won't have an iteration-method. But of course you can alwas do
this:

for i in xrange(len(l)):
x = l[i]
print x
print i
print "next"

Or - if len() can't be applied to your sequence for whatever reason, as it
is e.g. a iterable object, you can of course keep track with your own
counter:

i = 0
for x in some_iterable_t hingy:
print x
print i
i += 1
print "next"

Regards,

Diez

[Peter Otten]

Re: Get number of iteration

Florian Lindner wrote:
[color=blue]
> If I iterate through a list, is there a way I can get the number of the
> iteration: first, second, third, ...
>
> l = ["three", "four", "five", "six"]
> for x in l
> print x
> print x.iteration() # <- That's what I'm looking for!
> print "next"[/color]
[color=blue][color=green][color=darkred]
>>> sample = "tree for five".split()
>>> for index, item in enumerate(sampl e):[/color][/color][/color]
.... print index, item
....
0 tree
1 for
2 five

You are looking for enumerate(). Counting starts at 0, though.

Peter

[Sidharth Kuruvila]

Re: Get number of iteration

there is a function in python 2.3 called enumerate.

[color=blue][color=green][color=darkred]
>>> l = range(0,51,5)
>>> e = enumerate(range (0,51,5))
>>> e[/color][/color][/color]
<enumerate object at 0x0119BBC0>[color=blue][color=green][color=darkred]
>>> list(e)[/color][/color][/color]
[(0, 0), (1, 5), (2, 10), (3, 15), (4, 20), (5, 25), (6, 30), (7, 35), (8,
40), (9, 45), (10, 50)][color=blue][color=green][color=darkred]
>>> e = enumerate(range (0,51,5))
>>> for index, value in e:[/color][/color][/color]
.... print "The index of value %i is %i" % (value, index)
....
The index of value 0 is 0
The index of value 5 is 1
The index of value 10 is 2
..
..
..

if you are using an older version of python which doesn't have enumerate
you could do this[color=blue][color=green][color=darkred]
>>> l = range(0,51,5)
>>> zip(range(len(l )), l)[/color][/color][/color]
[(0, 0), (1, 5), (2, 10), (3, 15), (4, 20), (5, 25), (6, 30), (7, 35), (8,
40), (9, 45), (10, 50)]

[Sidharth Kuruvila]

Re: Get number of iteration

there is a function in python 2.3 called enumerate.

[color=blue][color=green][color=darkred]
>>> l = range(0,51,5)
>>> e = enumerate(range (0,51,5))
>>> e[/color][/color][/color]
<enumerate object at 0x0119BBC0>[color=blue][color=green][color=darkred]
>>> list(e)[/color][/color][/color]
[(0, 0), (1, 5), (2, 10), (3, 15), (4, 20), (5, 25), (6, 30), (7, 35), (8,
40), (9, 45), (10, 50)][color=blue][color=green][color=darkred]
>>> e = enumerate(range (0,51,5))
>>> for index, value in e:[/color][/color][/color]
.... print "The index of value %i is %i" % (value, index)
....
The index of value 0 is 0
The index of value 5 is 1
The index of value 10 is 2
..
..
..

if you are using an older version of python which doesn't have enumerate
you could do this[color=blue][color=green][color=darkred]
>>> l = range(0,51,5)
>>> zip(range(len(l )), l)[/color][/color][/color]
[(0, 0), (1, 5), (2, 10), (3, 15), (4, 20), (5, 25), (6, 30), (7, 35), (8,
40), (9, 45), (10, 50)]

[Skip Montanaro]

Re: Get number of iteration


Florian> If I iterate through a list, is there a way I can get the
Florian> number of the iteration: first, second, third, ...

Sure:
[color=blue][color=green][color=darkred]
>>> for i, what in enumerate(["three", "four", "five", "six"]):[/color][/color][/color]
... print i, what
...
0 three
1 four
2 five
3 six

Skip

[Jeff Epler]

Re: Get number of iteration

You're looking for the "enumerate" builtin function in 2.3.

for i, x in enumerate(l):
print x
print i
print "next"

You can define a "poor man's" enumerate in 2.2:

def enumerate(seq):
return zip(range(len(s eq)), l)

but the enumerate in 2.3 is an iterator, not a sequence.

Jeff

[Paul Prescod]

Re: Get number of iteration

Diez B. Roggisch wrote:
[color=blue][color=green]
>>If I iterate through a list, is there a way I can get the number of the
>>iteration: first, second, third, ...
>>
>>l = ["three", "four", "five", "six"]
>>for x in l
>> print x
>> print x.iteration() # <- That's what I'm looking for!
>> print "next"[/color]
> ...
>
> So usually x won't have an iteration-method. But of course you can alwas do
> this:
>
> for i in xrange(len(l)):
> x = l[i]
> print x
> print i
> print "next"[/color]

In recent versions of Python there is an easier way:
[color=blue][color=green][color=darkred]
>>> for index, value in enumerate(["three", "four", "five", "six"]):[/color][/color][/color]
.... print index, value
....
0 three
1 four
2 five
3 six

Paul Prescod

[Diez B. Roggisch]

Re: Get number of iteration

> In recent versions of Python there is an easier way:[color=blue]
>[color=green][color=darkred]
> >>> for index, value in enumerate(["three", "four", "five", "six"]):[/color][/color]
> ... print index, value
> ...
> 0 three
> 1 four
> 2 five
> 3 six[/color]

Boy, one never stops learning. I'll better stop answering here and read
only :)

Diez

[Jørgen Cederberg]

Re: Get number of iteration

Jeff Epler wrote:[color=blue]
> You're looking for the "enumerate" builtin function in 2.3.
>
> for i, x in enumerate(l):
> print x
> print i
> print "next"
>
> You can define a "poor man's" enumerate in 2.2:
>
> def enumerate(seq):
> return zip(range(len(s eq)), l)[/color]

Just nitpicking... :), but I guess you ment:

def enumerate(seq):
return zip(range(len(s eq)), seq)

/Jorgen

[Paul Rubin]

Re: Get number of iteration

Jørgen Cederberg <jorgencederber g@hotmail.com> writes:[color=blue]
> Just nitpicking... :), but I guess you ment:
>
> def enumerate(seq):
> return zip(range(len(s eq)), seq)[/color]

I think you want:

def enumerate(seq):
for i in xrange(len(seq) ):
yield (i, seq[i])