按值获取密钥，dict，python

Question

如何从值中获取密钥？

我的格言：

countries = {
        "Normal UK project" : "1",
        "UK Omnibus project" : "1-Omni",
        "Nordic project" : ["11","12","13","14"],
        "German project" : "21",
        "French project" : "31"
        }

我的半功能代码：

for k, v in countries.items():
    if "1" in v:
        print k

预期产量：

Normal UK project

实际产量：

French project
UK Omnibus project
German project
Normal UK project

我怎样才能修改我的代码？

Answer 1

c={}-任何dict
a（值）-需要知道这个密钥

key=list(c.keys())[list(c.values()).index(a)]]

Answer 2

问题是字典中的值类型不一样，这使得字典的使用更加困难，不仅仅是在这种情况下。虽然Python允许这样做，但您确实应该考虑统一字典中的类型，例如将它们全部列出来。只需一行代码即可：

countries = {key: val if isinstance(val, list) else [val] 
                        for key, val in countries.items()}

现在，每个字符串都被包装到一个列表中，您的现有代码将正常工作。

或者，如果必须使用当前形式的词典，则可以调整查找功能：

for k, v in countries.items():
    if "1" == v or isinstance(v, list) and "1" in v:
        print k

Answer 3

def keys_of_value(dct, value):
    for k in dct:
        if isinstance(dct[k], list):
            if value in dct[k]:
                return k
        else:
            if value == dct[k]:
                return k

assert keys_of_value(countries, "12") == "Nordic project"
assert keys_of_value(countries, "1")  == "Normal UK project"

如果你想让我缩短一点，我可以

from operator import eq, contains

def keys_of_value(dct, value, ops = (eq, contains)):
    for k in dct:
        if ops[isinstance(dct[k], list)](dct[k], value):
            return k

assert keys_of_value(countries, "12") == "Nordic project"
assert keys_of_value(countries, "1") == "Normal UK project"