python - 基于python中键值的2个字典列表中的2元组列表

Question

我有两个字典列表 lx 和 ly。 lx 的元素包含感兴趣的 key key1，ly 的元素包含 key2。我想创建一个二元组 (a,b) 列表，其中 a 是来自 lx 的字典，b 是来自 ly 这样 a['key1'] == b['key2']。有没有办法直接通过列表推导来做到这一点？

我失败的尝试是:

out = [(a,b) for a in lx for b in ly and a['key1'] == b['key2']]

但我收到“赋值前引用的局部变量 b”错误。

更新:

一个示例输入是:

lx = [{'key1': 'a', 'xyz': 1}, 
      {'key1': 'b', 'xyz': 2}, 
      {'key1': 'c', 'xyz': 3}]

ly = [{'key2': 'a', 'abc': '66'}, 
      {'key2': 'c', 'abc': '01'}]

输出:

out = [({'key1': 'a', 'xyz': 1}, {'key2': 'a', 'abc': '66'}), 
       ({'key1': 'c', 'xyz': 3}, {'key2': 'c', 'abc': '01'})]

Answer 1

您需要在条件之前使用if 而不是and:

>>> lx = [{'key1': 'foo'},  {'key1': 'foobar'}]
>>> ly = [{'key2': 'foo'},  {'key2': 'bar'}]
>>> [(a,b) for a in lx for b in ly and a['key1'] == b['key2']]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 1, in <listcomp>
UnboundLocalError: local variable 'b' referenced before assignment
>>> [(a,b) for a in lx for b in ly if a['key1'] == b['key2']]
[({'key1': 'foo'}, {'key2': 'foo'})]