[英]How to create array of objects in python
I'm creating a dictionary in python.我正在 python 中创建字典。 I'm getting same objects stored in dictionary while I loop through object.
当我循环通过 object 时,我将相同的对象存储在字典中。 Where am I doing wrong?
我在哪里做错了?
I tried dict()
, however, I'm avoiding dict()
.我尝试了
dict()
,但是,我避免dict()
。
Code I've tried is here:我试过的代码在这里:
image_dict = {}
#query for getting objects
images = Image_history.objects.all()
for image in images:
image_history = dict({
"type": image.image_type,
"timestamp": image.last_updated_timestamp,
})
image_dict.append(image_history)
My problem is when I use this following method to create dictionary in python:我的问题是当我使用以下方法在 python 中创建字典时:
image_dict = {}
image_list = {}
# list of image_details
image_list["image_details"] = []
#query for getting objects
images = Image_history.objects.all()
#looping through object and storing in dictionary
for image in images:
image_dict['type']= image.image_type
image_dict['timestamp']= image.last_updated_timestamp
#appending all those objects in loop to image_list
image_list["image_details"].append(image_dict)
I expect the output to be a list of different objects.我希望 output 是不同对象的列表。 But, I'm getting list of same duplicate objects.
但是,我得到了相同重复对象的列表。 Expected output:
预期 output:
{
"image_detail":[
{
"type": "png",
"timestamp": "1-12-18"
},
{
"type": "jpeg",
"timestamp": "1-1-19"
}
]
}
Actual output I'm getting:实际 output 我得到:
{
"image_detail":[
{
"type": "jpeg",
"timestamp": "1-1-19"
},{
"type": "jpeg",
"timestamp": "1-1-19"
}
]
}
Edit your code to:将您的代码编辑为:
image_list = {}
# list of image_details
image_list["image_details"] = []
#query for getting objects
images = Image_history.objects.all()
#looping through object and storing in dictionary
for image in images:
image_dict = {}
image_dict['type']= image.image_type
image_dict['timestamp']= image.last_updated_timestamp
#appending all those objects in loop to image_list
image_list["image_details"].append(image_dict)
Your are editing the same dictionary object, you just have to create new one at each iteration.您正在编辑同一个字典 object,您只需在每次迭代时创建一个新字典。 Dictionary (created using
dict
or {}
) is mutable objects in python, I suggest you read more about mutability in python.字典(使用
dict
或{}
创建)是 python 中的可变对象,我建议您阅读有关 python 中的可变性的更多信息。 And I suggest more compact way to build your list, using list comprehensions:我建议使用更紧凑的方式来构建您的列表,使用列表推导:
image_list["image_details"] = [
{
'type': image.image_type,
'timestamp': image.last_updated_timestamp
} for image in images
]
Note: you can create immutable dictionary in python, but this off-topic.注意:您可以在 python 中创建不可变字典,但这离题了。
You are mutating the same image_dict
object, which in turn modifies existing references to that object (ie previous dictionary values).您正在改变相同的
image_dict
object,这反过来又修改了对该 object 的现有引用(即以前的字典值)。
Why do you avoid constructing a new dict
?你为什么避免构建一个新的
dict
? It is the only way to create separate dictionaries.这是创建单独字典的唯一方法。
Alternatively you can move image_dict = {}
into the for
loop:或者,您可以将
image_dict = {}
移动到for
循环中:
...
for image in images:
image_dict = {}
image_dict['type']= image.image_type
...
You need to use a copy of image_history
dict as otherwise, you are just adding multiple references of the same dict.您需要使用
image_history
dict 的副本,否则,您只是添加了同一 dict 的多个引用。 In case of not using image_history.copy()
you will find each element in the image_dict
to have the same value as the last image object in the for
loop.在不使用
image_history.copy()
的情况下,您会发现 image_dict 中的每个元素与for
循环中的最后一个图像image_dict
具有相同的值。
Try the following.试试下面的。 I have used
dict.update()
.我用过
dict.update()
。 I am also using the index derived from enumeration of the images
.我还使用从
images
枚举中得出的索引。 An additional benefit of this approach is that you could easily load it up as a dataframe to view the data.这种方法的另一个好处是您可以轻松地将其加载为 dataframe 以查看数据。
image_dict = dict()
#query for getting objects
images = Image_history.objects.all()
for i, image in enumerate(images):
image_history = {
"type": image.image_type,
"timestamp": image.last_updated_timestamp,
}
image_dict.update({i: image_history.copy()})
# Optionally visualize the data in a dataframe
import pandas as pd
df = pd.DataFrame(image_dict).T
df.head()
Concise version of your code using dict comprehension.使用 dict 理解的代码的简洁版本。
# dict of image_history dicts
image_dict = dict((i, {"type": image.image_type,
"timestamp": image.last_updated_timestamp,
}) for i, image in enumerate(images))
Concise version of your code using list comprehension.使用列表理解的代码的简洁版本。
# list of image_history dicts
image_list = [{"type": image.image_type,
"timestamp": image.last_updated_timestamp,
}) for image in images)
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