Python functional programming: higher-order functions, Map/reduce

Python functional programming: higher-order functions, Map/reduce

1 #function-type programming2 #one feature of functional programming is that it allows the function itself to be passed as a parameter to another function, and also allows a function to be returned3 #(i) Higher order functions4 5f=ABS6 F7 Print(F (-20))8 #Results9 #A function can assign a value to a variable, namely: A variable can point to a functionTen #So what is the function name? The function name is actually a variable pointing to the function!  One  A #following the code, after execution, ABS has not pointed to an absolute value function but an integer of 10.  - #after the ABS (-10) will be error, unable to execute, you must restart Python.  - #abs=10 the #ABS ( -10) -  - #a simple high-order function - #The so-called higher order function, that is, the function can be passed as its parameters.  + defAdd (x,y,f): -     returnF (x) +f (Y) +  A Print(Add ( -5,6, ABS)) at  - #demonstrate higher order function map ()/reduce () - #The map () function receives two parameters, one is a function, and the other is a function that iterable,map the passed in sequence. - #acts on each element of the sequence and returns the result as a new iterator - #For example, we have a function f (x) =x^2, to effect it on a list[1,2,3,4,5,6,7,8,9] -  in deff (x): -     returnx*x toR=map (f,[1,2,3,4,5,6,7,8,9]) + #iterator is an iterator, which is an inert sequence that requires the list () function to calculate the entire sequence to return a list - Print(List (r)) the #results [1,4,9,16,25,36,49,64,81] *  $ #map () is a high-order function, in fact it abstracts the arithmetic rules. Panax Notoginseng #One more example, converting all of the list numbers to strings - Print(List (Map (str,[1,2,3,4,5,6,7,8]))) the #results [' 1 ', ' 2 ', ' 3 ', ' 4 ', ' 5 ', ' 6 ', ' 7 ', ' 8 '] +  A #reduce () function the #The effect of this is: + #reduce (f,[x1,x2,x3,x4]) =f (f (f (x1,x2), x3), x4) -  fromFunctoolsImportReduce $ deffn (x, y): $     returnx*10+y -  - Print(Reduce (fn,[1,3,5,7,9])) the #Result: 13579, which turns the sequence into an integer - Wuyi #Another example of implementing the function of the Int () function the defStr2Int (s): -     deffn (x, y): Wu         returnx*10+y -     defChar2num (s): About         return{'0'70A'1': 1,'2': 2,'3': 3,'4': 4, $                 '5'75A'6': 6,'7': 7,'8': 8,'9': 9}[s] -     returnReduce (Fn,map (char2num,s)) - Print(Str2Int ('784533')) - #result 784533 A  + #You can also use lambda functions to further simplify the the defChar2num (s): -     return{'0': 0,'1': 1,'2': 2,'3': 3,'4': 4, $             '5': 5,'6': 6,'7': 7,'8': 8,'9'8 {}[s] the defStr2Int (s): the     returnReduceLambdax,y:x*10+Y,map (char2num,s)) the Print(Str2Int ('743092')) the #result 743092

Python functional programming: higher-order functions, Map/reduce