递归地合并dict，以便将具有共享密钥的元素组合到lis中

Question

我有两个口头禅要合并：

a = {"name": "john",
     "phone":"123123123",
     "owns": {"cars": "Car 1", "motorbikes": "Motorbike 1"}}

b = {"name": "john",
     "phone":"123",
     "owns": {"cars": "Car 2"}}

如果a和{}在同一嵌套级别上有一个公共键，则结果应该是一个列表，其中包含两个值，该列表被指定为共享密钥的值。在

结果应该如下所示：

^{pr2}$

使用a.update(b)无效，因为它用b的共享值覆盖{}的共享值，结果如下：

{'name': 'john', 'phone': '123', 'owns': {'cars': 'Car 2'}}

目标是合并dict而不重写，并保留与特定键相关的所有信息（在两个dict中）。在

Answer 1

使用集合和事物，还可以合并任意数量的词典：

from functools import reduce
import operator

# Usage: merge(a, b, ...)
def merge(*args):
    # Make a copy of the input dicts, can be removed if you don't care about modifying
    # the original dicts.
    args = list(map(dict.copy, args))

    # Dict to store the result.
    out = {}

    for k in reduce(operator.and_, map(dict.keys, args)):  # Python 3 only, see footnotes.
        # Use `.pop()` so that after the all elements of shared keys have been combined,
        # `args` becomes a list of disjoint dicts that we can merge easily.
        vs = [d.pop(k) for d in args]

        if isinstance(vs[0], dict):
            # Recursively merge nested dicts
            common = merge(*vs)
        else:
            # Use a set to collect unique values
            common = set(vs)
            # If only one unique value, store that as is, otherwise use a list
            common = next(iter(common)) if len(common) == 1 else list(common)

        out[k] = common

    # Merge into `out` the rest of the now disjoint dicts
    for arg in args:
        out.update(arg)

    return out

假设要合并的每个字典具有相同的“结构”，因此"owns"不能是a中的列表和{}中的dict。dict的每个元素也需要是散列的，因为这个方法使用集合来聚合唯一的值。在

---

下面的代码只适用于python3，因为在python2中，dict.keys()返回一个普通的旧列表。在

^{pr2}$

另一种方法是添加一个额外的map()，将列表转换为集合：

reduce(operator.and_, map(set, map(dict.keys, args)))