根据另一个字典列表中的键值删除字典

Question

I have a list of dictionaries and a main dictionary. List of dictionaries have the following format. Values are assigned a variable that changes dynamically in the program.

list_dict = [{'url': url_value , 'title' : title_value}, {'url': url_value , 'title' : title_value}]

main_dict = {"execution_time": "2017-06-05", "target_url": "http://www.bloomberg.com", "data": [{ "url" : url1}, { "url" : url2}], "name": "Michael", "occupation": "software"}

If any url value(url1 or url2) under data in main_dict is the same value as the url_value in any of the dictionaries in list_dict, I want to delete that dictionary from the data.

Output: Assuming url_value is url1 then:

main_dict = {"execution_time": "2017-06-05", "target_url": "http://www.bloomberg.com", "data": [{ "url" : url2}], "name": "Michael", "occupation": "software"}

I thought about using dict comprehensions, however everything I tried did not work. I would appreciate a starting point or any guidance.

Answer 1

This should do the trick:

my_list = [list_dict_data['url'] for list_dict_data in list_dict]
delete_list = []

for i in range(len(main_dict['data'])):
  if main_dict['data'][i]['url'] in my_list:
    delete_list.append(i)

for i in delete_list:
  del main_dict['data'][i]

So what it does is:

1. List all the urls to check from list_dict
2. Iterate through all the urls in main dict and compare it with the data in list_dict
3. Add the index to the delete list
4. Iterate through the delete list and delete the corresponding index in main_dict

Try optimising this though as its really crude.

Answer 2

You can try this:

>>> list_dict = [{'url': "url1" , 'title' : "title_value1"}, {'url': "other_url" , 'title' : "title_value2"}]
>>> main_dict = {"execution_time": "2017-06-05", "target_url": "http://www.bloomberg.com", "data": [{ "url" : "url1"}, { "url" : "url2"}], "name": "Michael", "occupation": "software"}
>>> S = set(d["url"] for d in list_dict)
>>> main_dict["data"] = [d for d in main_dict["data"] if d["url"] not in S]
>>> main_dict
{'execution_time': '2017-06-05', 'target_url': 'http://www.bloomberg.com', 'data': [{'url': 'url2'}], 'name': 'Michael', 'occupation': 'software'}

Instead of deleting elements of main_dict["data"] , the idea is to recreate the list without the matchings urls:

• extract the distinct urls of the list_dict in S ;
• filter the dicts d in main_dict["data"] on the rule: d["url"] not in S .

Note on naming: try to name your variables according to the content and not the type .

• list_dict is a list of dictionaries (I can see it), but I would like to know immediately what's in those dictionaries. web_pages would be better, if you accept that an url + a title makes a page. But you should specify why those pages are on this list (eg dead_link_pages , or whatever)
• main_dict is a dictionary (pretty obvious and not really informative): something like task is better. Again, a better specification is informative: update_task , retrieve_task , ?
• ok, I replace S by page_urls !

Have a look, this is far more readable:

>>> web_pages = [{'url': "url1" , 'title' : "title_value1"}, {'url': "other_url" , 'title' : "title_value2"}]
>>> task = {"execution_time": "2017-06-05", "target_url": "http://www.bloomberg.com", "data": [{ "url" : "url1"}, { "url" : "url2"}], "name": "Michael", "occupation": "software"}
>>> page_urls = set(p["url"] for p in web_pages)
>>> task["data"] = [t for t in task["data"] if t["url"] not in page_urls]
>>> task
{'execution_time': '2017-06-05', 'target_url': 'http://www.bloomberg.com', 'data': [{'url': 'url2'}], 'name': 'Michael', 'occupation': 'software'}