day 15 two built-in functions recursively lamda sorted filter map dichotomy evaluation

 The main contents of today
1. lambda anonymous function
　　syntax:
　　　　the lambda parameters: return value
　　　　can not perform complex operations can only write a single line

2. sorted () function ordering

　　sorted(iterable, key =None ,reverse=false)

　　sorted (iterables, key = None, reverse = False)

= LST [1,3,23,6,4,34,23,12,9] 
lst.sort () is a list inside a #sort method 
Print (LST) 
the sorted (LST) # built-in function, a back to you the new list, the new list is sorted. (And dic.frokeys ()) the same effect,　　
Print (LST)

　　Sort.

　　　　1. iterables
　　　　2. key = function. Collation
　　　　3. reverse. Whether reverse

　　Principle: Each element in the interior will be sorted iteration object passed to this function key parameters, sorted according to the output of the function. For example: the length can be sorted list of strings

3. filter () function filters

　　filter (function, iterable) is dealt a iterator

　　Principle: The iterator objects each element is passed to a function, and is determined according to the function returns True or False if this data is preserved

　　　　1. The function returns True or False
　　　　2. iterables

 

4. map () function mapping

  　　map (function, iterable) is a processed iterator

　　Principle: can be mapped to the iterator object in each element, respectively, and then performs function
　　　　1. Function
　　　　2 iterables

5 . Recursive
　　　　calls itself.
　　　　　　DEF FUNC ():
　　　　　　　　FUNC ()
　　　　　　FUNC ()

　　　　Uses: traverse the tree
　　　　difficult: the need to find a bad think the law is not good read.

Traversing the tree structure 
Import OS 
filePath = "D: \ Sylar \ python_workspace" 
DEF Read (filePath, n-): 
    IT = the os.listdir (filePath) # open the folder 
    for EL in IT: 
        # get path 
        fp = os.path .join (filePath, el) # to get the absolute path 
        if os.path.isdir (fp): # determine whether the folder 
            Print ( "\ t" the n-*, EL) 
            the Read (fp, the n-+ 1) is # continue to read the folder contents of the internal recursive entrance. 
        the else: 
            Print ( "\ t" the n-*, EL) # recursive export 
read (filePath, 0)

 

 

6. dichotomy
　　end pinch head takes an intermediate. Constantly changing the left and right. Indirectly change the center.

　　Query efficiency is very high, but the limitations of relatively large, must be ordered sequence before you can use binary search