[英]Python: select dictionary items by key
I have this dictionary: 我有这本字典:
a = {
'car1': ('high cp', 'low fd', 'safe'),
'car2': ('med cp', 'med fd', 'safe'),
'car3': ('low cp', 'high fd', 'safe'),
'taxi1': ('high cp', 'low fd', 'safe', 'med wt'),
'taxi2': ('high cp', 'low fd', 'safe', 'high wt'),
'taxi3': ('high cp', 'low fd', 'safe', 'high wt')
}
From the above dictionary, I want to create a new dictionary that consists only 'car%s' 从以上字典中,我想创建一个仅包含“ car%s”的新字典
I'm using this code snippet (from another question) 我正在使用此代码段 (来自另一个问题)
b = {}
for key in a:
if key == 'car%s'% (range (4)):
print (" %s : %s" % (key, a[key]))
print(b)
It returns {} 它返回{}
I expect to get: 我希望得到:
a = {
'car1': ('high cp', 'low fd', 'safe'),
'car2': ('med cp', 'med fd', 'safe'),
'car3': ('low cp', 'high fd', 'safe'),
}
What am I missing here? 我在这里想念什么?
If you want to add keys which contain word car
in it, then it will work: 如果要添加其中包含单词
car
键,则它将起作用:
a = {
'car1': ('high cp', 'low fd', 'safe'),
'car2': ('med cp', 'med fd', 'safe'),
'car3': ('low cp', 'high fd', 'safe'),
'taxi1': ('high cp', 'low fd', 'safe', 'med wt'),
'taxi2': ('high cp', 'low fd', 'safe', 'high wt'),
'taxi3': ('high cp', 'low fd', 'safe', 'high wt')
}
b = {}
for key in a:
if 'car' in key:
print (key, a[key])
b[key] = a[key]
print(b)
You're checking the prefix the wrong way and you're not storing the result. 您正在以错误的方式检查前缀,并且没有存储结果。 You could use
str.startswith
and dict comprehension to generate the result: 您可以使用
str.startswith
和dict comprehension生成结果:
>>> a = {
... 'car1': ('high cp', 'low fd', 'safe'),
... 'car2': ('med cp', 'med fd', 'safe'),
... 'car3': ('low cp', 'high fd', 'safe'),
... 'taxi1': ('high cp', 'low fd', 'safe', 'med wt'),
... 'taxi2': ('high cp', 'low fd', 'safe', 'high wt'),
... 'taxi3': ('high cp', 'low fd', 'safe', 'high wt')
... }
>>> res = {k: v for k, v in a.items() if k.startswith('car')}
>>> res
{'car2': ('med cp', 'med fd', 'safe'), 'car3': ('low cp', 'high fd', 'safe'), 'car1': ('high cp', 'low fd', 'safe')}
Instead of inserting a number to the format string your current check inserts the range
object there which probably isn't the result you expect: 当前的检查不是在格式字符串中插入数字,而是在其中插入
range
对象,这可能不是您期望的结果:
>>> 'car%s'% (range (4))
'carrange(0, 4)'
You never do anything with the keys you validate but print
them. 您永远不会对已验证的密钥进行任何操作,而是
print
它们。 You need to add them to your new dictionary: 您需要将它们添加到新词典中:
b ={}
for key, val in a.items(): # .iteritems() for Python 2.x users
if key == 'car%s' % (range (4)):
b[key] = val
print(b)
Your code is would still be broken however. 您的代码仍然会被破坏。 You need to make some changes:
您需要进行一些更改:
"car"
. "car"
。 Forget trying to match the whole string. This entire for loop could be made into a very simple dictionary comprehension: 整个for循环可以做成一个非常简单的字典理解:
>>> a = { ... 'car1': ('high cp', 'low fd', 'safe'), ... 'car2': ('med cp', 'med fd', 'safe'), ... 'car3': ('low cp', 'high fd', 'safe'), ... 'taxi1': ('high cp', 'low fd', 'safe', 'med wt'), ... 'taxi2': ('high cp', 'low fd', 'safe', 'high wt'), ... 'taxi3': ('high cp', 'low fd', 'safe', 'high wt') ... } >>> {k: v for k, v in a.items() if k[0:3] == 'car'} {'car2': ('med cp', 'med fd', 'safe'), 'car3': ('low cp', 'high fd', 'safe'), 'car1': ('high cp', 'low fd', 'safe')} >>>
This works: 这有效:
new_dict = {}
for k in a.keys():
if 'car' in k:
new_dict[k] = a[k]
result: 结果:
>>new_dict
{'car1': ('high cp', 'low fd', 'safe'),
'car2': ('med cp', 'med fd', 'safe'),
'car3': ('low cp', 'high fd', 'safe')}
what do you expect from range(4)? 您对range(4)有什么期望? It returns
[0, 1, 2, 3]
返回
[0, 1, 2, 3]
b = {}
for key in range(4):
new_key = "car%s" % key # generate new_key
item = a.get(new_key)
if item is not None:
b[new_key] = item
print (b)
OR you want to get items only starts with car
, read this link https://docs.python.org/3/library/stdtypes.html#str.startswith 或者您只想让商品以
car
开头,请阅读此链接https://docs.python.org/3/library/stdtypes.html#str.startswith
b = {}
for key, value in a.items():
if key.startswith("car"):
b[key] = a[key]
print (b)
output 输出
{'car2': ('med cp', 'med fd', 'safe'),
'car3': ('low cp', 'high fd', 'safe'),
'car1': ('high cp', 'low fd', 'safe')}
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