python - 在python中查找数组中的索引

Question

我看过 Finding the index of an item given a list containing it in Python

我还没有找到解决办法。我有一个附加了 426 个值的列表，我正在寻找“KORD”的索引，但它声称它不在列表中，而实际上是这样。

metar_txt = open("metar.txt", "r") 
lines = metar_txt.readlines() 
for line in lines: 
    if len(line) > 20: 
        stations = []
        stations.append(line.split(' ')[0])
        print stations.index('KORD')
metar_txt.close()

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-34-9271d129d452> in <module>()
      5         stations = []
      6         stations.append(line.split(' ')[0])
----> 7         print stations.index('KORD')
      8 metar_txt.close()

ValueError: 'KORD' is not in list

Answer 1

在循环外创建列表，您仅将列表中的单个元素存储为 stations = []在循环中不断创建一个空列表，然后添加一个元素，重复每次迭代:

stations = []
for line in lines: 
    if len(line) > 20:

如果您每次都在循环中调用索引，那么除非您在第一次迭代中添加子字符串，否则您将不断收到索引错误，不确定您的目标是什么，但我想在循环完成时进行索引工作:

with open("metar.txt", "r")  as metar_txt:
    stations = []
    for line in metar_txt: 
        if len(line) > 20: 
            stations.append(line.rstrip().split(' ')[0]
    print stations.index('KORD') # outside loop

如果你只是想要它出现的位置的索引，那么当你去的时候只增加计数 if len(line) > 20是 True 这与在循环结束时尝试在列表中查找子字符串索引完全相同:

with open("metar.txt", "r")  as metar_txt:
    stations = []
    i = 0
    for line in metar_txt:
        if len(line) > 20:
            w = line.rstrip().split(' ')[0]
            if w == "KORD":
                print(i)
            i += 1

最后，如果你想为多个单词保留一些索引记录，你可以使用字典，这样找到的索引将为 0(1):

with open("metar.txt", "r")  as metar_txt:
    stations = {}
    i = 0
    for line in metar_txt:
        if len(line) > 20:
            w = line.rstrip().split(' ')[0]
            stations[w] = i
            i += 1
print(stations["KORD"])

如果您想要高效查找并保持顺序，您可以使用 OrderedDict :

from collections import OrderedDict
with open("metar.txt", "r")  as metar_txt:
    stations = OrderedDict()
    i = 0
    for line in metar_txt:
        if len(line) > 20:
            w = line.rstrip().split(' ')[0]
            stations[w] = i
            i += 1

所以 for st in stations:print(st)将按照添加的顺序输出站和stations["word"]会给你索引。

或者像 Jon 评论的那样使用 genexp 和 str.partition:

from collections import OrderedDict
with open("metar.txt", "r")  as metar_txt:
 lines = (line.partition(' ')[0] for line in metar_txt if len(line) > 20)
 stations = OrderedDict((el, idx) for idx, el in enumerate(lines))

或使用 itertools.count使用单个 genexp:

with open("metar.txt", "r")  as metar_txt:
    from itertools import count
    cn = count()
    stations = OrderedDict((line.rstrip().split(' ')[0], next(cn))
                           for line in metar_txt if len(line) > 20)