将不同的字典合并到一个列表中

Question

I have created 4 different sets of dictionaries with the guidance of this post: Python variables as keys to dict . I now want to merge all these dictionaries into 1 list. I tried the following:

classes = ['apple', 'orange', 'pear', 'mango']
class_dict = {}
store = []

for fruit in classes:
    if fruit == "orange":
        o = 2
        q = 1
    else:
        o = 0
        q = 0

    for j in ('fruit', 'o', 'q'):
        class_dict[j] = locals()[j]
    print (class_dict)
    store.append(class_dict)
print ("store: ", store)

The output is as shown below. As you can see, store only contains a list of the same dictionary being appended to it each time. I'm not sure where I'm going wrong and some help on this would be much appreciated!

{'fruit': 'apple', 'o': 0, 'q': 0}
{'fruit': 'orange', 'o': 2, 'q': 1}
{'fruit': 'pear', 'o': 0, 'q': 0}
{'fruit': 'mango', 'o': 0, 'q': 0}

store:  [{'fruit': 'mango', 'o': 0, 'q': 0}, {'fruit': 'mango', 'o': 0, 'q': 0}, {'fruit': 'mango', 'o': 0, 'q': 0}, {'fruit': 'mango', 'o': 0, 'q': 0}]

Answer 1

You need to move your class_dict inside the loop.

classes = ['apple', 'orange', 'pear', 'mango']

store = []

for fruit in classes:
    class_dict = {}
    if fruit == "orange":
        o = 2
        q = 1
    else:
        o = 0
        q = 0

    for j in ('fruit', 'o', 'q'):
        class_dict[j] = locals()[j]
    print (class_dict)
    store.append(class_dict)
print ("store: ", store)

output:

{'fruit': 'apple', 'o': 0, 'q': 0}
{'fruit': 'orange', 'o': 2, 'q': 1}
{'fruit': 'pear', 'o': 0, 'q': 0}
{'fruit': 'mango', 'o': 0, 'q': 0}
store:  [{'fruit': 'apple', 'o': 0, 'q': 0}, {'fruit': 'orange', 'o': 2, 'q': 1}, {'fruit': 'pear', 'o': 0, 'q': 0}, {'fruit': 'mango', 'o': 0, 'q': 0}]

Answer 2

You should just move class_dict inside the loop:

classes = ['apple', 'orange', 'pear', 'mango']

store = []

for fruit in classes:
    class_dict = {}
    if fruit == "orange":
        o = 2
        q = 1
    else:
        o = 0
        q = 0

    for j in ('fruit', 'o', 'q'):
        class_dict[j] = locals()[j]
    print (class_dict)
    store.append(class_dict)
print ("store: ", store)

It's because dict is a mutable object in python and in every iteration of your for loop you change the value of the global variable class_dict . The simple example of it:

>>> a = {'a': 1, 'b': 2}
>>> a
{'a': 1, 'b': 2}
>>> b = a
>>> b
{'a': 1, 'b': 2}
>>> b['c'] = 3
>>> b
{'a': 1, 'b': 2, 'c': 3}
>>> a
{'a': 1, 'b': 2, 'c': 3}

When you move class_dict inside the loop, this variable becomes local and iterations of the loop become independent.