遍历并删除python词典列表中的某些元素

Question

I have json file that looks like this:

[{'Events': [{'EventName': 'Log',
              'EventType': 'Native',
              'LogLevel': 'error',
              'Message': 'missing event: seqNum=1'},
             {'EventName': 'Log',
              'EventType': 'Native',
              'LogLevel': 'error',
              'Message': 'missing event: seqNum=2'}],
  'Id': 116005},
 {'Events': [{'EventName': 'Log',
              'EventType': 'Native',
              'LogLevel': 'error',
              'Message': 'missing event: seqNum=101'},
             {'EventName': 'Log',
              'EventType': 'Native',
              'LogLevel': 'error',
              'Message': 'missing event: seqNum=102'},
             {'BrowserInfo': {'name': 'IE ', 'version': '11'},
              'EventName': 'Log',
              'EventType': 'Native',
              'LogLevel': 'info',
              'SeqNum': 3,
              'SiteID': 1454445626890,
              'Time': 1454445626891,
              'URL': 'http://test.com'},
             {'BrowserInfo': {'name': 'IE ', 'version': '11'},
              'EventName': 'eventIndicator',
              'EventType': 'responseTime',
              'SeqNum': 8,
              'SiteID': 1454445626890,
              'Time': 1454445626923,
              'URL': 'http://test.com'}],
  'Id': 116005}]

And I am trying to remove each of the events where "EventName": "Log" .

I would assume there is a way to pop them out, but I can't even iterate far enough into the list to do that. What is the cleanest way to do this?

I should end up with a list that looks like:

[{'Events': [{'BrowserInfo': {'name': 'IE ', 'version': '11'},
              'EventName': 'eventIndicator',
              'EventType': 'responseTime',
              'SeqNum': 8,
              'SiteID': 1454445626890,
              'Time': 1454445626923,
              'URL': 'http://test.com'}],
  'Id': 116005}]

Answer 1

It's difficult to modify a list or other data structure as you're iterating over it. It's often easier to create a new data structure, excluding the unwanted values.

You appear to want to do two things:

1. Remove dictionaries from the "Events" lists that have an "EventName" of "Log" .
2. Remove any top level dictionaries who's lists of events have become empty after the "Log" events were removed.

It's a bit tricky to do both at once, I but not too bad:

filtered_json_list = []
for event_group in json_list:
    filtered_events = [event for event in event_group["Events"]
                             if event["EventName"] != "Log"]
    if filtered_events: # skip empty event groups!
        filtered_json_list.append({"Id": event_group["Id"], "Events": filtered_events})

This was a lot easier than I expected because the top-level dictionaries (which I call event_group s, for lack of a better name) only had two keys, "Id" and "Events" . If instead there were many keys and values in those dictionaries (or which keys and values they had were unpredictable), you'd probably need to replace the last line of my code with something more complicated (eg creating a dictionary with just the filtered events, then using kind of loop to copy over all the non- "Events" keys and values), rather than creating the dictionary by hand with a literal.

Answer 2

This program might help.

import json

# Parse the JSON
with open('x.json') as fp:
    events = json.load(fp)


# Kill all "Log" events
for event_set in events:
    event_list = event_set['Events']
    event_list[:] = [event for event in event_list if event['EventName'] != 'Log']

# Kill all empty event sets
events[:] = [event_set for event_set in events if event_set['Events']]

print json.dumps(events, indent=2)

Answer 3

您可以为此使用Python生成器/列表理解

[x for x in json where x['EventName'] != 'Log']