Index confusion in python

Question

Hello folks am new to python development.I have wrote a sample code:

mylist = ['something','baby','car']
for i,n in mylist:
    mylist[i] = mylist[i]+1
    print i,n

I know i is the index in the list so it will execute up to the number of elements in the list.But when I execute the script I get type error...

In this code the index of the list is inceremented by one... So the expected result is.

0 something
1 baby
2 car

Instead of that i got a typeerror..Please help me in solving this..Any help would be appreciated..Thanks

C.B. · Accepted Answer · 2014-04-07 14:19:15Z

3

Very close, just missing enumerate--

for i,n in enumerate(mylist):

However, the code above will attempt to add an integer to a string; this will throw a new error. If you are trying to push elements back, you would want mylist[i] = mylist[i+1] (note you would have to have a case to catch the last element)

edited Apr 7, 2014 at 14:19

answered Apr 7, 2014 at 14:12

C.B.

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3 Comments

sshashank124 Over a year ago

@user3501595, Alternatively, you can do: for i in mylist: and then print i,mylist[i]

C.B. Over a year ago

@sshashank124 do you mean for i in range(0,len(mylist)): ?

bruno desthuilliers Over a year ago

Since we have enumerate, there are few reasons (well, good reasons I mean) to use for i in range(len(mylist)):. The above use case is definitly not one of them.

bruno desthuilliers · Accepted Answer · 2014-04-07 14:23:42Z

0

This :

mylist = ['something','baby','car']
for i,n in mylist:
    mylist[i] = mylist[i]+1
    print i,n

raises a ValueError ("Too many values to unpack") on the second line.

If you just add enumate on this second line, ie for i,n in enumerate(mylist):, then you get a TypeError on the next line, because you are trying to add a string (mylist[i]) and an integer (i). The point is: what you want to increment is i, not mylist[i] (which is the same thing as n fwiw), so it should be:

for i, n in enumerate(mylist):
    i = i + 1
    print i, n

BUT you don't have to go thru such complications to print out "index+1 : item at index+1", all you need is to pass the optional start argument to enumerate:

mylist = ['something','baby','car']
for i, n in enumerate(mylist, 1):
    print i, n

answered Apr 7, 2014 at 14:23

bruno desthuilliers

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3 Comments

user3501595 Over a year ago

so what will be the result is i give mylist[i] ..is it possible in python ?...can you tell me its use ?

bruno desthuilliers Over a year ago

@user3501595 : this is fully documented, you know. cf docs.python.org/2/tutorial/introduction.html#lists and docs.python.org/2/reference/… for a start.

user3501595 Over a year ago

thanks ..and can you tell me in which situation do i wanna add mylist[i] = mylist[i]+1...Please ..

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