Python's closures

If in an intrinsic function, a reference is made to a variable that is in an outer scope (but not at the global scope), then the intrinsic function is considered a closure (closure).  variables defined within an external function but referenced or used by an intrinsic function are called free variables.

Closures are an important concept in functional programming, and Scheme and Haskell are two of the functional programming. Closures are syntactically simple (as simple as internal functions) but still powerful.

So why would you want to use closures?
Closures are useful for installing calculations, hiding states, and switching freely between function objects and scopes.

closures in gui< Span class= "FONTSTYLE0" > or in many api event-driven programming that supports callback functions is useful. data.   callback is a function. Closures are also functions, but they can carry some additional scopes.   additional scopes.
Closures and function calls are not much related, but rather about using variables defined in other scopes.

 def  counter (start_at=0): Count  =< Span style= "color: #000000;" >[START_AT]  def   INCR (): Count[0]+=1 return   Count[0]  return   incr;  if  __name__  ==  __main__   :  print  (Counter (0) ()) 

counter () The only thing to do is to accept an initialized value to start counting and assign that value to the list count the only member. Then define an intrinsic function that incr () by using the variable internally count We created a closure because it now carries the entire counter () incr () increased the running count

And then the last magic is counter () returns a incr, a (callable ) function object.

Note Counter (0) (), counter (0) returns the INCR, a callable function object, so add () later

Python's closures