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why for loop print only once after add if statement

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  why for loop print only once after add if statement jobmattcon@gmail.com - 2016-05-28 03:19 -0700
    Re: why for loop print only once after add if statement Sayth Renshaw <flebber.crue@gmail.com> - 2016-05-28 03:49 -0700
    Re: why for loop print only once after add if statement Peter Otten <__peter__@web.de> - 2016-05-28 13:54 +0200
    Re: why for loop print only once after add if statement Steven D'Aprano <steve@pearwood.info> - 2016-05-28 22:02 +1000
    Re: why for loop print only once after add if statement meInvent bbird <jobmattcon@gmail.com> - 2016-05-28 05:31 -0700
    Re: why for loop print only once after add if statement meInvent bbird <jobmattcon@gmail.com> - 2016-05-28 05:35 -0700
    Re: why for loop print only once after add if statement Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2016-05-28 12:59 -0400

#109199 — why for loop print only once after add if statement

for item, i in enumerate(aa)
  print item

this writing, it can print all values

for item, i in enumerate(aa)
  if item == findit:
    print item

this only print the first value, means it only print once then not print again,

where is wrong?

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#109201

On Saturday, 28 May 2016 20:19:23 UTC+10, meInvent bbird  wrote:
> for item, i in enumerate(aa)
>   print item
> 
> this writing, it can print all values
> 
> for item, i in enumerate(aa)
>   if item == findit:
>     print item
> 
> this only print the first value, means it only print once then not print again,
> 
> where is wrong?

Enumerate is there to get rid of the i its not need enumerate is a generator.

list(enumerate(aa, start=1))

https://docs.python.org/3/library/functions.html#enumerate

In [1]: aa = range(10)

In [2]: list(enumerate(aa, start=1))
Out[2]: 
[(1, 0),
 (2, 1),
 (3, 2),
 (4, 3),
 (5, 4),
 (6, 5),
 (7, 6),
 (8, 7),
 (9, 8),
 (10, 9)]

Sayth

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#109202

jobmattcon@gmail.com wrote:

> for item, i in enumerate(aa)
>   print item
> 
> this writing, it can print all values
> 
> for item, i in enumerate(aa)
>   if item == findit:
>     print item
> 
> this only print the first value, means it only print once then not print
> again,

Assuming

aa = ["foo", "bar", "baz"]

and

findit = "bar"

the print statement will only be executed when findit == item.

First iteration of your for loop:

item = "foo"
if "foo" == "bar": # False
   print "foo"     # not executed, nothing printed

Second iteration:

item = "bar"
if "bar" == "bar": # True
    print "bar"    # prints bar

Third iteration:

item = "baz"
if "baz" == "bar": # False
    print "baz"    # not executed, nothing printed

> where is wrong?

This depends on what you want to achieve. Can you tell us?

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#109203

On Sat, 28 May 2016 08:19 pm, jobmattcon@gmail.com wrote:

> for item, i in enumerate(aa)
>   print item

Wrong way around. It should be:

for i, item in enumerate(aa):
    print item

For example:

py> for i, item in enumerate(aa):
...     print i, item
...
0 c
1 h
2 e
3 e
4 s
5 e


> this writing, it can print all values
> 
> for item, i in enumerate(aa)
>   if item == findit:
>     print item
> 
> this only print the first value, means it only print once then not print
> again,

No, it doesn't not print the first value, it prints any value that equals
findit, whatever that is. If nothing equals findit, nothing will be
printed. Only items which equal findit will be printed.


py> findit = 'z'
py> for i, item in enumerate(aa):
...     if item == findit:
...             print i, item
...
py> findit = 'e'
py> for i, item in enumerate(aa):
...     if item == findit:
...             print i, item
...
2 e
3 e
5 e


-- 
Steven

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#109205

thanks, i discover that i misunderstand i and item,

they should be swapped

On Saturday, May 28, 2016 at 6:19:23 PM UTC+8, meInvent bbird wrote:
> for item, i in enumerate(aa)
>   print item
> 
> this writing, it can print all values
> 
> for item, i in enumerate(aa)
>   if item == findit:
>     print item
> 
> this only print the first value, means it only print once then not print again,
> 
> where is wrong?

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#109207

when read my code again, i discover this error i fixed before

but forget to do for another branch of if statement

now fixed

On Saturday, May 28, 2016 at 6:19:23 PM UTC+8, meInvent bbird wrote:
> for item, i in enumerate(aa)
>   print item
> 
> this writing, it can print all values
> 
> for item, i in enumerate(aa)
>   if item == findit:
>     print item
> 
> this only print the first value, means it only print once then not print again,
> 
> where is wrong?

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#109216

On Sat, 28 May 2016 03:19:10 -0700 (PDT), jobmattcon@gmail.com declaimed
the following:

>for item, i in enumerate(aa)
>  print item
>
>this writing, it can print all values
>
>for item, i in enumerate(aa)
>  if item == findit:
>    print item
>
>this only print the first value, means it only print once then not print again,
>
>where is wrong?

	First thought...

	for i, item in enumerate(aa):

	The first term is the (zero-base) index and the second is the actual
item value.

	No idea what "findit" is, so can't do any further testing, nor what
"aa" contains.

>>> aa = "alcoholics anonymous"
>>> for stuff in enumerate(aa):
... 	print stuff
... 	
(0, 'a')
(1, 'l')
(2, 'c')
(3, 'o')
(4, 'h')
(5, 'o')
(6, 'l')
(7, 'i')
(8, 'c')
(9, 's')
(10, ' ')
(11, 'a')
(12, 'n')
(13, 'o')
(14, 'n')
(15, 'y')
(16, 'm')
(17, 'o')
(18, 'u')
(19, 's')
>>> 

>>> for i, v in enumerate(aa):
... 	if v == "o":
... 		print i
... 
3
5
13
17
>>> 
-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
    wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/

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