Built-in functions added:
map: map
map (func, iterables) ----> map objects
Each map will be the value of the iteration modify object, then the object map in a map, the map object may then be converted into lists / tuples,
Note that only one revolution (after the primary reason is to take the generator was taken over)
# Map map NAME_LIST = [ ' Egon ' , ' Jason ' , ' Sean ' , ' cake ' , ' Tank ' ] map_obj = Map ( the lambda X: X + ' _dsb ' IF ! X = ' Tank ' the else X + ' like oysters ' , NAME_LIST) Print (map_obj) # map_obj may become list / tuple type Print (List (map_obj)) # map_obj ----> generator (iterator) ---- "after use, can not get the Print (tuple (map_obj))
reduce: Merge
When using the first call reduce module
from functools import reduce
Obtaining two values from each iteration may be merged object, functions are performed reduce starts from an initial value of the combined
reduce (function address, iterables, the initial value (default 0))
# The reduce Merge from functools import reduce print(reduce(lambda x, y: x+y, range(1, 101), 0)) result: 5050
filter: filter
filer (function address, iterables) ----> filter objects
Results returned by the filter will function in the corresponding filter parameter value to True out, filtered off value is added to the filter object
xx_dsb.endswith ( '_ dsb'): Returns True or False
# Filter filtering NAME_LIST = [ ' egn_dsb ' , ' jason_dsb ' , ' sean_dsb ' , ' cake _dsb ' , ' Tank ' ] filter_obj = filter ( the lambda name: name.endswith ( ' _dsb ' ), NAME_LIST) Print (filter_obj) Print (List (filter_obj)) Print (tuple (filter_obj)) # empty tuple, has been taken over the list above
Recursive function (to know):
Recursive function refers to the repeated "direct or indirect" call the function itself, which is an expression of nested function calls form
Direct call: it refers to the built-in function, direct call function itself
Indirect calls: Calls between two mutually recursive functions indirectly caused
Learn:
Python recursive default depth: 998,1000 (limit the number of recursion)
However, each operating system will set the default recursion depth based on hard disk
import sys # acquisition module operating system resources
Get recursion depth: print (sys.getrecursionlimit ())
Set recursion depth: print (sys.setresursionlimit (2000)) (depth value)
# View the current value of the recursion depth
Note: There is no sense of time alone recursive call
Want recursive meaningful, must comply with two conditions:
- back:
Refers repeatedly performed, the results of each execution must get closer to a result, there must be a termination condition backtracking
- Deduction:
After backtracking to find a termination condition, start up step by step recursion
+ 2 = age4 age5 age4 = 2 + Age3 Age3 = Age2 +2 Age2 = +2 AGE1 AGE1 = 18 is # back termination results
#result = age (n-1) +2
From top to bottom is backtracking process, from the bottom up process is recursive
DEF Age (the n-): IF the n-== 1 : return 18 return Age (the n--1) +2 # must write the return can be achieved recursive age ()
Module
What is a module?
Module is a combination of a series of functions
One module is essentially equivalent to the file # py wrapped stack of modules and function codes
Module Source:
1, Python built-in module (Python interpreter)
For example: sys / time / os / tutle
2, third-party modules (written by someone else)
For example: request
3, custom modules (write your own)
For example: you define demo.py file
Manifestations modules:
1, written in Python py file (understand)
2, compiled DLL or shared library in C or C ++ libraries (understanding)
3, following a set of packet py files with the _lnit_.py
-py_demo
-_init_.py
-demo.py
-demo2.py
What is the package?
Refers to the internal packet contains a folder __init__.py
py file in the Python interpreter:
1) file in the folder Python interpreter
2) one of the py file
Why use two modules?
Module can help us better manage the function codes, such as: function ...
may be split into a number of functional items were stored in different py files (modules) in.
Three how to create, write module and use the module?
- Right-click the file to create py
- py write python code file
- In a file by keyword import import module
import module name
# Note: When you import the module, the module can not add the suffix .py
- the use of the module stage, it must be noted, who is the executable file, who is import the file (module to be introduced)
- module on the first import, it has been fixed, the order of the current file is the first look to find memory
- what happens when you import the module:
1. will first execute the currently executing file and generate the executable file name space.
2. When the execution code into the module, the module is introduced will produce a module namespace.
3 will be introduced into the module namespace loaded into memory.
- to the module from the alias as
Import module as an alias module
- introducing a modular manner
- import module
- direct execution file import Imports
- from the package / module import module / (function name, variable name, class name)
- directly in the executable file import Import
- Import circulation problems:
- model1.py from model2 import name name = 'jason' - model2.py from model1 import name name = 'tank'
- Import problem solving cycle:
1. The need to find the name on the import module above
2. Import Inside the function, the module becomes a function namespace name
- Software development directory specification:
Note: Every time writing project, must create a new folder with the project must be allowed to project folder as the project root directory.
- Project file folder
- conf:
- used to store configuration files folder
- Core:
- Core business code .py
- interface:
- Interface, within the interface logic to write code before data acquisition, after the adoption in order to obtain data
- db:
- used to store file data
- lib:
- public function to store files
- log:
- used to store the log file, a log for recording the user's operation
- bin:
- stored inside the boot file / - startup file
- the Readme.txt:
- project description, the user tells the operator the user program