[英]if else nested for loops using python list comprehension
Can anyone help me figure the list comprehension way of producing following output - 谁能帮我找出产生以下输出的列表理解方式-
Let given list be - 让给定列表为-
results = [
{"id": 1, "name": "input"},
{"name": "status", "desc": "Status"},
{"name": "entity", "fields": [
{"id": 101, "name": "value"},
{"id": 102, "name": "address"}]
}
]
And I am looking for output in the form of list. 我正在寻找列表形式的输出。 The code to get the output is: 获得输出的代码是:
output = []
for eachDict in results:
if "fields" in eachDict:
for field in eachDict["fields"]:
output.append(eachDict["name"]+"."+field["name"])
else:
output.append(eachDict["name"])
Thus the output using above code is - 因此,使用上述代码的输出是-
['input', 'status', 'entity.value', 'entity.address']
Is it possible to get similar output using if else nested for loops in list Comprehension? 如果在列表理解中嵌套了for循环,是否有可能获得类似的输出?
I am having trouble trying to get access to that inner for loop in if condition of list Comprehension 如果列表理解的条件,我在尝试访问该内部for循环时遇到麻烦
My attempt - 我的尝试-
output = [eachDict["name"]+"."+field["name"] for field in eachDict["fields"] if "fields" in eachDict else eachDict["name"] for eachDict in results]
One way to transform your code into workable code would be to make the inner loop produce lists, and then flatten the result afterward. 将您的代码转换为可行代码的一种方法是使内部循环产生列表,然后将结果展平。
sum(([d['name'] + '.' + f['name'] for f in d['fields']]
if d.get('fields') else [d['name']] for d in results), [])
A list comprehension has a fixed number of (nested) loops. 列表推导具有固定数量的(嵌套)循环。 So must have two loops here, one over the top-level dictionaries, and one over the fields
. 因此,这里必须有两个循环,一个在顶级字典上,另一个在fields
。 The trick is to produce one iteration in the nested loop if there are no fields: 诀窍是如果没有字段,则在嵌套循环中产生一个迭代:
[d['name'] + fieldname
for d in results
for fieldname in (
('.' + sub['name'] for sub in d['fields']) if 'fields' in d else
('',))
]
The for fieldname
loop loops either over the names of the fields
sub-directories (with '.'
prefixed), or over a tuple with just a single empty string in it. 在for fieldname
回路循环要么在名称fields
子目录(用'.'
前缀), 或在与它只是一个空字符串的元组。
Note that this isn't actually all that readable. 请注意,这实际上并不是所有可读性。 I'd delegate producing the fieldname loop to a helper generator function to improve that: 我将产生fieldname循环委托给一个辅助生成器函数来改善这一点:
def fieldnames(d):
if 'fields' in d:
for sub in d['fields']:
yield '.' + sub['name']
else:
yield ''
[d['name'] + fieldname for d in results for fieldname in fieldnames(d)]
Demo: 演示:
>>> def fieldnames(d):
... if 'fields' in d:
... for sub in d['fields']:
... yield '.' + sub['name']
... else:
... yield ''
...
>>> [d['name'] + fieldname for d in results for fieldname in fieldnames(d)]
['input', 'status', 'entity.value', 'entity.address']
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