在Python中使用元组查找列表中的元素

Question

I have a little complicated data and want to find specific element with key tuple. target tuple is a little different from key , because it has an id property. So I cannot use key in target .

So what's the best way to implement smart searching in this case?

targets = [
    {"id": 0, "X": (), "Y": (), "Z": () },
    {"id": 1, "X": (1,), "Y": (5,), "Z": ()},
    {"id": 2, "X": (1,), "Y": (5, 7), "Z": ()},
    {"id": 3, "X": (2,), "Y": (5, 7), "Z": (1,)},
    {"id": 4, "X": (1, 2), "Y": (5, 7), "Z": (1,)},
    {"id": 5, "X": (1, 2), "Y": (5, 7), "Z": (1,3)},
]

key = {"X": (1,), "Y": (5, 7), "Z": ()}

I want to implement find method to extract expected slot like below.

In []: find(targets, key)
Out[]: {'id': 2, 'X': (1,), 'Y': (5, 7), 'Z': ()}

Answer 1

If the key-value pairs must match exactly, you can use Dictionary view objects to treat the key-value pairs as sets . You want to find a strict subset :

def find(targets, key):
    for target in targets:
        if key.items() < target.items():
            return target

This finds the first match only.

You could turn this into a one-liner:

next((target for target in targets if key.items() < target.items()), None)

If you must produce all matches, you can replace return with yield in the above method to turn it into a generator, or you could use a list comprehension:

[target for target in targets if key.items() < target.items()]

The above uses Python 3 syntax. In Python 2, dictionary views are available through the special .viewkeys() , .viewvalues() and .viewitems() methods, so add in view to the method name:

def find(targets, key):
    # Python 2 version
    for target in targets:
        if key.viewitems() < target.viewitems():
            return target

Demo (on Python 3):

>>> targets = [
...     {"id": 0, "X": (), "Y": (), "Z": () },
...     {"id": 1, "X": (1,), "Y": (5,), "Z": ()},
...     {"id": 2, "X": (1,), "Y": (5, 7), "Z": ()},
...     {"id": 3, "X": (2,), "Y": (5, 7), "Z": (1,)},
...     {"id": 4, "X": (1, 2), "Y": (5, 7), "Z": (1,)},
...     {"id": 5, "X": (1, 2), "Y": (5, 7), "Z": (1,3)},
... ]
>>> key = {"X": (1,), "Y": (5, 7), "Z": ()}
>>> def find(targets, key):
...     for target in targets:
...         if key.items() < target.items():
...             return target
...
>>> find(targets, key)
{'Y': (5, 7), 'X': (1,), 'Z': (), 'id': 2}
>>> next((target for target in targets if key.items() < target.items()), None)
{'Y': (5, 7), 'X': (1,), 'Z': (), 'id': 2}
>>> [target for target in targets if key.items() < target.items()]
[{'Y': (5, 7), 'X': (1,), 'Z': (), 'id': 2}]