Python notes-----higher-order functions

1, sorted (sort object, key=): The Sort object can be a category, or a string and a dictionary, key is a custom sort, such as: "Key=abs, sorted by absolute value" "Key=lambda x:x[1", sorted by the second value of the sorted object, if it is a two-dimensional array, The second dimension row, if the dictionary is ranked by the value "

①sorted (Sort object, Key=abs):

Value:key=abs "Sort by absolute value"

String: The default is to sort by lowercase to uppercase. key=str.lower"turn all strings into lowercase and reorder" eg:sorted ([' A ', ' dob ', ' Cold ', Zoo '], key=str.lower) Result: ' A ', ' Cold ', ' DOB ', ' Zoo ' "

Dictionary type (two-dimensional array): Fromoperator import Itemgetter

　　　　　　　　　　　　　Key=itemgetter (1)

　　　　　　　　　　　　　Or

Key=lambda X:x[1]

②sorted (Sort object, reverse=true): reverse order

2. Map (function, iterator): Perform the same function operation on an iterator.

Such as:

List (map (str,[1,2,3,4,5))

Result: "' 1 ', ' 2 ', ' 3 ', ' 4 ', ' 5 '" so you don't have to use for to loop through.

3. Reduce (function, iterator): Iterate over each element in an iterator, such as SUM, Maximum minimum .....

4. Map and reduce combine to convert a string ' 13579 ' into an integer 13579

 from Import reducea=reduce (lambda x,y:x*10+y,map (int,'13579'))

5, filter (function f, iterator L): Filter function, the value returned after the function f is true or has a value is returned, if False or empty does not return the value.

def is_odd (n):     return n% 2 = = 1list (filter (is_odd, [1, 2, 4, 5, 6, 9, 10, 15]))

　　

Python notes-----higher-order functions