- Derive an expression
- yield Usage
- Module concept and method for introducing
- Packages and package management
Derived expression (using for, one by one into data )
List comprehension
Derivation collection
Derivation dictionary
Iterator
Iteration
for the iteration variable in iterable
Each cycle will automatically let 'iteration variable "points" to the next element. "
The method of generating iterator
travel () __iter __ ()
The value
next(iterator) iterator.__next__()
Note: If, after the iterator value to take complete, it will return an error StopIteration
Iterator object itself needs to support the following two methods, which together form the iterator protocol
iterator.__iter__() iterator.__next__()
Generates an iterator from iterables
Iterator = iter (iterables)
The next value = next (iterator)
for implementation principle
Custom iterator
Builder
Builder will not suddenly put it out of content generation, () with the next generation to use when needed
Method a: deriving a list of the formula [] into ()
Method two: function inside with yield
yield operating rules
yiled an object 1, return the object 2, 3 pause function, wait for the next next Reactivate
note
yield expression can only be used in the function
yield expression can function as a generator
yield expression can return a result, and execute tentative function, until the next activation yield a
Simply understanding generator is a iterator
Python using generators to delay operations provide support
so-called latency operations, refers only produce results when needed, rather than produce immediate results, thus saving a lot of space, which is the generator of the main benefits
Modules and packages
There are three methods of introducing
import package name
from a package name import module name, module name 2, ...
In the same directory, the above two methods can be used to directly introducing
In different directories, use sys.path.append ( 'path') adding the path, the path is added to the sys.path
Module
In python, the module is a py file
Packages and package management
Package concept: many modules into the inside of a folder, a package can be formed
Package Manager: When the many modules in a file, in order to facilitate package module references, the introduction of package management
__init__.py
In package management added this module, the packet attribute name can be directly accessed through the access object within this module
python2 must be added, pyhton3 can also be used without the
Specification is to add the file content may be empty
Introducing relative path
In the package management, respectively, can be introduced into the same layer and the upper layer through the module. (A dot) and .. (two points)
Usage: from .module (.. module) import obj
Introducing effect: in a package, if the package module to import other modules in the same package, it is necessary to use this method for introducing
After introduction Effect: When this occurs a manner import module, the module can not be run directly, it can be introduced into