[英]Searching for Key, Value in a list of dictionaries
回答问题:
经过一番帮助,我意识到它正在崩溃,因为它正在扫描电子邮件,而当一封电子邮件可以满足我的需求时,其余的却没有,因此导致其崩溃。
添加Try / Except解决了该问题。 仅出于历史原因,以防其他任何人寻找类似的问题,这是有效的代码。
try:
if (item for item in list_of_dict if item['name'] == "From" and item['value'] == 'NAME1 <name@some_email.com>').next():
print('has it')
else:
pass
except StopIteration:
print("Not found")
通过这种方式,它可以扫描每封电子邮件,并在发生故障时进行错误处理,但是,如果发现它可以打印,我将找到所需的内容。
原始问题:
码:
if (item for item in list_of_dict if item['name'] == "From" and item['value'] == 'NAME1 <name1@some_email.com>').next()
我收到一个StopIteration
错误:
Traceback (most recent call last):
File "quickstart1.py", line 232, in <module>
main()
File "quickstart1.py", line 194, in main
if (item for item in list_of_dict if item['name'] == "From" and item['value'] == 'NAME1 <name1@some_email.com>').next():
StopIteration
这是我的代码:
if (item for item in list_of_dict if item['name'] == "From" and item['value'] == 'NAME1 <name1@some_email.com>').next():
print('has it')
else:
print('doesnt have it')
当我检查我是否错误地放入迭代器时,我对item ['value']进行了查找:
print((item for item in list_of_dict if item['name'] == "From").next())
返回值:
{u'name': u'From', u'value': u'NAME1 <name1@some_email.com>'}
{u'name': u'From', u'value': u'NAME2 <name2@some_email.com>'}
只需通过and
添加另一个条件:
next(item for item in dicts if item["name"] == "Tom" and item["age"] == 10)
请注意,如果没有匹配项, next()
将抛出StopIteration
异常,您可以通过try/except
进行处理:
try:
value = next(item for item in dicts if item["name"] == "Tom" and item["age"] == 10)
print(value)
except StopIteration:
print("Not found")
或者,提供默认值 :
next((item for item in dicts if item["name"] == "Tom" and item["age"] == 10), "Default value")
如果要检查是否有任何字典,可以使用next
的默认参数:
iter = (item for item in list_of_dict if item['name'] == "From" and item['value'] == 'name <email>')
if next(iter, None) is not None: # using None as default
print('has it')
else:
print('doesnt have it')
但这也将排除None
常规项目,因此您也可以使用try
和except
:
try:
item = next(iter)
except StopIteration:
print('doesnt have it')
else:
print('has it') # else is evaluated only if "try" didn't raise the exception.
但是请注意,生成器只能使用一次,因此,如果要再次使用它,请重新创建该生成器:
iter = ...
print(list(iter))
next(iter) # <-- fails because generator is exhausted in print
iter = ...
print(list(iter))
iter = ...
next(iter) # <-- works
dicts = [
{ "name": "Tom", "age": 10 },
{ "name": "Pam", "age": 7 },
{ "name": "Dick", "age": 12 }
]
super_dict = {} # will be {'Dick': 12, 'Pam': 7, 'Tom': 10}
for d in dicts:
super_dict[d["name"]]=d['age']
if super_dict["Tom"]==10:
print 'hey, Tom is really 10'
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