Printing specific items out of a list

问题

I'm wondering how to print specific items from a list e.g. given:

li = [1,2,3,4]

I want to print just the 3^rd and 4^th within a loop and I have been trying to use some kind of for-loop like the following:

for i in range (li(3,4)):
    print (li[i])

However I'm Getting all kinds of error such as:

TypeError: list indices must be integers, not tuple.
TypeError: list object is not callable

I've been trying to change () for [] and been shuffling the words around to see if it would work but it hasn't so far.

回答1:

Using slice notation you can get the sublist of items you want:

>>> li = [1,2,3,4]
>>> li[2:]
[3, 4]

Then just iterate over the sublist:

>>> for item in li[2:]:
...     print item
... 
3
4

回答2:

You should do:

for i in [2, 3]:
    print(li[i])

By range(n), you are getting [0, 1, 2, ..., n-1]

By range(m, n), you are getting [m, m+1, ..., n-1]

That is why you use range, getting a list of indices.

It is more recommended to use slicing like other fellows showed.

回答3:

li(3,4) will try to call whatever li is with the arguments 3 and 4. As a list is not callable, this will fail. If you want to iterate over a certain list of indexes, you can just specify it like that:

for i in [2, 3]:
    print(li[i])

Note that indexes start at zero, so if you want to get the 3 and 4 you will need to access list indexes 2 and 3.

You can also slice the list and iterate over the lists instead. By doing li[2:4] you get a list containing the third and fourth element (i.e. indexes i with 2 <= i < 4). And then you can use the for loop to iterate over those elements:

for x in li[2:4]:
    print(x)

Note that iterating over a list will give you the elements directly but not the indexes.

来源：https://stackoverflow.com/questions/20609376/printing-specific-items-out-of-a-list

标签

python

list

printing