can I get the index number in for x in y loop?

[JuHui]

a='String'.... print x
....
S
t
r
i
n
g
can I get the index number of a in the upon loop within for x in a
loop?

 

[Luigi]

Try this:
.... print i, x
.... i+=1
....
0 S
1 t
2 r
3 i
4 n
5 g

 

[Paul McGuire]

... print x
...
S
t
r
i
n
g

can I get the index number of a in the upon loop within for x in a
loop?

Use enumerate. See example below.

-- Paul
.... print x
....
S
t
r
i
n
g.... print x
....
(0, 'S')
(1, 't')
(2, 'r')
(3, 'i')
(4, 'n')
(5, 'g')

 

[Rune Strand]

... print x
...
S
t
r
i
n
g

can I get the index number of a in the upon loop within for x in a
loop?

for x, y in enumerate(a)
print x, y

 

[JuHui]

which one has best performance?

a:for i in range(0,len(a))
b:for x in a
c:for x,y in enumerate(a)

but, it seems I cann't get index number with b format..

 

[Felipe Almeida Lessa]

Em Seg, 2006-04-03 às 08:47 -0700, JuHui escreveu:

which one has best performance?

Let's see...

a:for i in range(0,len(a))

$ python2.4 -mtimeit -s 'a=[None]*100' 'for i in range(len(a)):
j = a
'
100000 loops, best of 3: 17.7 usec per loop

$ python2.4 -mtimeit -s 'a=[None]*100' 'for i in xrange(len(a)):
j = a
'
100000 loops, best of 3: 16.8 usec per loop

b:for x in a

$ python2.4 -mtimeit -s 'a=[None]*100' 'i = 0
for j in a:
i += 1
'
100000 loops, best of 3: 15.7 usec per loop

c:for x,y in enumerate(a)

$ python2.4 -mtimeit -s 'a=[None]*100' 'for i, j in enumerate(a):
pass
'
100000 loops, best of 3: 12.9 usec per loop


Using enumerate is cleaner and faster.

HTH,

 

[JuHui]

thanks a lot!

 

[Scott David Daniels]

which one has best performance?

a:for i in range(0,len(a))
b:for x in a
c:for x,y in enumerate(a)

Read up on the timeit module and figure it out for yourself.
The answer will depend on the distribution of your data.

> but, it seems I can't get index number with b format..

Well, that's true, but it is a bit like saying:

I cannot find the distance in meters between Paris and London with:
for i in range(10):
print i

--Scott David Daniels
(e-mail address removed)

 

[John Hunter]

Scott> I cannot find the distance in meters between Paris and
Scott> London with: for i in range(10): print i

Works for me

def range(x):
yield '332.8 km'

for i in range(10):
print i

....may not be considered best practice, though <wink>

JDH

 

[Fuzzyman]

... print x
...
S
t
r
i
n
g

can I get the index number of a in the upon loop within for x in a
loop?

Although enumerate is the 'right' answer, I personally prefer :


i = 0
while i < len(some_sequence):
val = some_sequence
...
i += 1

This is so that I can manually wind 'i' backwards and forwards manually
from other parts of the code.

Fuzzyman
http://www.voidspace.org.uk/python/index.shtml