How can I access each element of a pair in a pair list?

问题

I have a list called pairs.

pairs = [("a", 1), ("b", 2), ("c", 3)]

And I can access elements as:

for x in pairs:
    print x

which gives output like:

('a', 1) ('b', 2) ('c', 3)

But I want to access each element in each pair, like in c++, if we use pair<string, int> we are able to access, first element and second element by x.first, and x.second.eg.

x = make_pair("a",1)
x.first= 'a'
x.second= 1

How can I do the same in python?

回答1:

Use tuple unpacking:

>>> pairs = [("a", 1), ("b", 2), ("c", 3)]
>>> for a, b in pairs:
...    print a, b
... 
a 1
b 2
c 3

回答2:

If you want to use names, try a namedtuple:

from collections import namedtuple

Pair = namedtuple("Pair", ["first", "second"])

pairs = [Pair("a", 1), Pair("b", 2), Pair("c", 3)]

for pair in pairs:
    print("First = {}, second = {}".format(pair.first, pair.second))

回答3:

A 2-tuple is a pair. You can access the first and second elements like this:

x = tuple('a', 1) # make a pair
x[0] # access 'a'
x[1] # access 1

回答4:

When you say pair[0], that gives you ("a", 1). The thing in parentheses is a tuple, which, like a list, is a type of collection. So you can access the first element of that thing by specifying [0] or [1] after its name. So all you have to do to get the first element of the first element of pair is say pair[0][0]. Or if you want the second element of the third element, it's pair[2][1].

回答5:

You can access the members by their index in the tuple.

lst = [(1,'on'),(2,'onn'),(3,'onnn'),(4,'onnnn'),(5,'onnnnn')]

def unFld(x):

    for i in x:
        print(i[0],' ',i[1])

print(unFld(lst))

Output :

1    on

2    onn

3    onnn

4    onnnn

5    onnnnn

来源：https://stackoverflow.com/questions/22496657/how-can-i-access-each-element-of-a-pair-in-a-pair-list

标签

python

list

tuples