I'm new to python. Please anyone help me to understand this statement of python. How it will work ?
{x: {y: 0. for y in myClass.features} for x in myClass.items}
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Can you please post some code preceding this line of codeAgile_Eagle– Agile_Eagle2018-07-21 12:05:47 +00:00Commented Jul 21, 2018 at 12:05
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It's not a for-loop, but a (nested) dict comprehension. See e.g.: python.org/dev/peps/pep-0274 or stackoverflow.com/questions/14507591/…user2390182– user23901822018-07-21 12:09:24 +00:00Commented Jul 21, 2018 at 12:09
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2 Answers
Basically what it do is to create a nested dictionary with all values equal to 0.0
class myClassrino:
def __init__(self):
self.features=[1,2,3,4,5]
self.items=[3,4,5,6]
myClass=myClassrino()
output={x: {y: 0. for y in myClass.features} for x in myClass.items}
print(output)
Output is:
{3: {1: 0.0, 2: 0.0, 3: 0.0, 4: 0.0, 5: 0.0}, 4: {1: 0.0, 2: 0.0, 3: 0.0, 4: 0.0, 5: 0.0}, 5: {1: 0.0, 2: 0.0, 3: 0.0, 4: 0.0, 5: 0.0}, 6: {1: 0.0, 2: 0.0, 3: 0.0, 4: 0.0, 5: 0.0}}
Feel free to post anything you are still unclear..
3 Comments
star123
thank you. y : 0 here : is equal to assignment operator or what ?
Marcus.Aurelianus
@y : 0 equal to d[y]=0, you can check it out here. docs.python.org/3/library/stdtypes.html#mapping-types-dict
Marcus.Aurelianus
Consider accept the answer by clicking the check on the left of question, it will remove the this from review queue, save other moderators time and distribute the points around.
Just give it a try.
{x: {y: 0. for y in [1,2,3]} for x in ['a','b','c']}
=
{'a': {1: 0.0, 2: 0.0, 3: 0.0}, 'b': {1: 0.0, 2: 0.0, 3: 0.0}, 'c': {1: 0.0, 2: 0.0, 3: 0.0}}
Then ones can have some feeling about it from the output.
To be easier, you can decompose it:
{y: 0. for y in [1,2,3]}
=
{1: 0.0, 2: 0.0, 3: 0.0}
after substitution, we have
{x: {1: 0.0, 2: 0.0, 3: 0.0} for x in ['a','b','c']}
final answer =
{'a': {1: 0.0, 2: 0.0, 3: 0.0}, 'b': {1: 0.0, 2: 0.0, 3: 0.0}, 'c': {1: 0.0, 2: 0.0, 3: 0.0}}
Now you only need to replace
[1,2,3] and ['a','b','c']
to
myClass.features and myClass.items
Both are implicitly declared by defining them.
Sorry for my poor expression.
1 Comment
star123
Thank you. You explained very well