Generator
Generator generator: A mechanism for calculating one side of the loop.A generator is a special program that can be used to control the iterative behavior of loops. The builder in Python is one of the iterators that use the yield return value function, which is paused each time the yield is called, and t
The builder is one of the most difficult concepts for Python novice developers to understand, although it is considered a high-level skill in Python programming, but in a variety of projects you can see the builder everywhere, you have to understand it, use it, and even love it.When it comes to generators, it's inevitable to pull the iterator out of the way, the generator is a very similar object to the iterator, and if the iterator is compared to an
equilateral, the rectangle is a square, and so on.Obviously, if an object is made up of many components, we cannot hard code in the construction method to meet the requirements of the various users on the structure of the component. Therefore, in the abstract-oriented principle, we should not do any coding in the Geometry class construction method, but instead divide the construction method of the geometry class object into several steps, that is to define several methods in one port according
· Python · use a generator and iterator to implement your own xrange Disclaimer: This article is published by love butterfly at http://blog.csdn.net/lanphaday. all rights are available. Welcome to download this article. The statement should be reprinted. Thank you.
Those who have used Python must be familiar with the following two lines:
Code : >>> For I in xrange (0, 10, 1 ):
Print I The above two lines of code print the 10 numbers 0-9 in a loop.
Parse the generator in Python and its differences with the iterator.
GeneratorA generator is an iterator and a special function. It is constructed into an iterator using the yield operation. A common function has an entry and a return value. When a function is called, it is executed from the entry and the return value is returned at the end. The function defined by the
What is a generator?A generator is a function that contains the special keyword yield. When called, the generator function returns a generator. You can use the send, throw, and close methods to allow the generator to interact with the outside world.
The
Python learning diary: day13 ------ iterator and generator, pythonday13 ------I. Import 1. the dir function print (dir ([]) tells me that all the methods in this list contain double underscores. 2. The returned value after a list executes _ iter _ () is an iterator 3, the number of _ length_hint _ elements 4, and the value of _ setstate _ from the specified position is 5, []. _ iter _ () iterator ----> _ next _ you can use next to get values from the
()) # Print (i.__next__ ()) # Print (i.__next__ ()) # Print (i.__next__ ()) #StopIteration Iterator determines whether an iterator object iterabl is required to iterate over the object as an iterative object. __iter__ () is converted to an iterator to iterate over an iterator object that can iterate the iterator directly to the application: 1 provides a unified iterative Method 2 lazy computation that does not depend on the index, For example, to fetch each line of a fileIv.
, 8, 12]]This in turn writes the same as follows:transposed = []for i in Range (4): transposed_row = [] for row in matrix: transposed_row.append (Row[i]) Transposed.append (transposed_row) Print transposed# [[1, 5, 9], [2, 6, 10], [3, 7, 11], [4, 8, 12]]There is also a python built-in function zip (), also can be implemented as above functionZip (*matrix) # [(1, 5, 9), (2, 6, 10), (3, 7, 11), (4, 8, 12)]2.del statement (The DEL statement)>>> a = [-1, 1, 66.25, 333, 333, 1234.5]>>
exactly the same:>>> for N in Fab (5): ... Print N ... 1 1 2) 3 5 Simply put, the function of yield is to turn a function into a generator, the function with yield is no longer a normal function, the Python interpreter treats it as a generator, and the Call to FAB (5) does not execute the FAB function, but instead returns a Iterab Le Object! When the For loop executes, each loop executes the code
The following small series will bring you an in-depth understanding of python function recursion and generator. I think this is quite good. now I will share it with you and give you a reference. Let's take a look at it with Xiaobian.
1. what is recursion?
If a function contains a call to itself, the function is recursive. Recursion is an algorithm widely used in programming languages. it usually converts a large and complex problem into a small prob
Based on the revision and source code analysis of mybatis-generator-core 1.3.5, mybatisgeneratorcoreProject Description
Mybatis-generator is used to generate code files such as entity classes based on database tables and fields. During the National Day, I analyzed the mybatis-generator-core source code and wrote quite detailed Chinese comments. Let's take a look.
first, the new test projectCreate a new MAVEN project MybatisDemo2, modify Pom.xml to introduce dependencies. Dependencies added on the previous sectionDependency> groupId>Org.mybatis.generatorgroupId> Artifactid>Mybatis-generator-coreArtifactid> version>1.3.2version>Dependency>Build Add PluginBuild> Plugins> plugin> groupId>Org.mybatis.generatorgroupId> Artifactid>Mybatis-
Python [5]-generative, generator, and python generativeI. Condition and loop 1. if statement
If
For example:
age=5if age>=18: print 'adult'elif age>=6: print 'teenager'else: print 'kid'
Be sure to pay attention to the colon at the end of the Condition Statement and the indentation of the code segment.
As long as the if parameter is a non-zero value, non-empty string, non-empty list, etc., it is determinedTrueOtherwiseFalse.2. Loop
Range (num): Re
Tornado 4.0 has been released for a long time, and the new version has widely applied the Future feature. We have now upgraded the Tornado to the latest version, and have also used a lot of the coprocessor features.
A long time no update blog, today is a simple introduction to the implementation of the Tornado, the Tornado is based on the Python generator implementation, so first of all to review the generator
__next__() methodsNote: For an iterator object, the __iter__ method is executed, and the result is still itself
5. Advantages and disadvantages of iterators
Advantages:1. Provides an iterative approach that does not rely on subscript2. More memory savings on the drop iterator itselfDisadvantages:1. Unable to get the length of the iterator object2. The value of the sequence type is flexible, is a one-time, can only be taken back to the value, not forwardSecond,
http://www.cnblogs.com/qixiaoyizhan/p/7597315.html "Preface"Using Mybatis-generator to automatically generate DAO, Model, mapping related files, the role of Mybatis-generator is to act as a code generator, and using code generators not only simplifies our workload, Productivity is improved, and the probability of code errors can be greatly reduced. In the SSM (Sp
: ret.append (expr)Example: for inch if and i%3==for ifif i%3==0]the use of a list-resolved multilayer loop:A list of analytic expressions:[Expr for I in Iterable1 for J in Iterable2]Natural notation:ret = [] for in iterable1: for in iterable2: Ret.append (expr)Example[(x, Y) forXinch 'ABCDE' forYinchRange (3)][[x, y] forXinch 'ABCDE' forYinchRange (3)][{x:y} forXinch 'ABCDE' forYinchRange (3)]Generator e
1. Generator functionsThe difference between a generator function and a normal function is that1. Use yield instead of return in the generator function, and yield can be called multiple times2. When the function runs to yield, the yield current state is preserved, waiting for the next nextUsage examples: def Test (): yield 1 yield 2 yield 3a=test () b=
List Builder is a very simple but very powerful built-in python.Generate a list [1,2,3,4] can use list (range (1,5))Application of List BuilderIf the above formula is judged, you can filter out the desired result, such as just the square of the even numberUsing multi-layer loopsGeneratorThe essential difference between a generator and a list generator is that one has generated data, and when used, it genera
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