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Python

Vincent Zamora
Vincent Zamora
3,872 Points
Posted by Vincent Zamora
Vincent Zamora
3,872 Points

Dictionary Comprehensions

I am trying to figure out what this code does, but I am not having any luck:

fields: Dict[str, DataMember] = {x: getattr(cls, x, None) for x in dir(cls) if isinstance(getattr(cls, x, None), DataMember)}

[MOD: added ```python formatting. -cf]

2 Answers

Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 68,441 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,441 Points

Rewriting the original code:

fields: Dict[str, DataMember] = {x: getattr(cls, x, None) for x in dir(cls) if isinstance(getattr(cls, x, None), DataMember)}

as

fields: Dict[str, DataMember] = {x: getattr(cls, x, None)
                                for x in dir(cls)
                                if isinstance(getattr(cls, x, None), DataMember)
                               }

the elements:

  • dir(cls) returns a list of attributes of cls
  • for x in dir(cls) cycles over this list assigning the attribute name to x
  • getattr(cls, x, None) retrieves the value of the attribute, if it exists, or returns None
  • isinstance(object, Class) returns True if object is an instance of Class.
  • Together, isinstance(getattr(cls, x, None), DataMember) returns True if the attribute x contains an instance of class DataMember
  • finally, x: getattr(cls, x, None) associates key name x with the object attribute x if it is an instance of DataMember

Post back if you need more help. Good luck!