编写一个使用 try...except 处理 KeyError 的函数，然后将其用作 key 参数，而不是您的lambda。

def extract_time(json):
        # Also convert to int since update_time will be string.  When comparing
        # strings, "10" is smaller than "2".
        return int(json['page']['update_time'])
    except KeyError:
        return 0
# lines.sort() is more efficient than lines = lines.sorted()
lines.sort(key=extract_time, reverse=True)

您可以使用具有默认值的 dict.get() ：

lines = sorted(lines, key=lambda k: k['page'].get('update_time', 0), reverse=True)

示例：

>>> lines = [
...     {"page": {"url": "url1", "update_time": "1415387875"}, "other_key": {}},
...     {"page": {"url": "url2", "update_time": "1415381963"}, "other_key": {}},
...     {"page": {"url": "url3", "update_time": "1415384938"}, "other_key": {}},
...     {"page": {"url": "url4"}, "other_key": {}},
...     {"page": {"url": "url5"}, "other_key": {}}
... ]
>>> lines = sorted(lines, key=lambda k: k['page'].get('update_time', 0), reverse=True)
>>> for line in lines:
...     print line