考虑一下——基类a，类B继承自a，类C继承自B，在初始化器中调用父类初始化器的通用方法是什么?如果这听起来仍然太模糊，这里有一些代码。

class A(object):
    def __init__(self):
        print "Initialiser A was called"

class B(A):
    def __init__(self):
        super(B,self).__init__()
        print "Initialiser B was called"

class C(B):
    def __init__(self):
        super(C,self).__init__()
        print "Initialiser C was called"

c = C()

我现在就是这么做的。但它似乎还是有点太非泛型了——您仍然必须手动传递正确的类型。

现在，我尝试使用self。__class__作为super()的第一个参数，但是，显然它不起作用-如果你把它放在C的初始化式中-很好，B的初始化式会被调用。如果你在B中做同样的事情，“self”仍然指向C的一个实例，所以你最终再次调用B的初始化式(这以无限递归结束)。

目前没有必要考虑钻石继承的问题，我只是对解决这个具体问题感兴趣。

因此，由于我一直在使用Spring，如果我要编写一个有依赖关系的服务，我会这样做:

@Component
public class SomeService {
     @Autowired private SomeOtherService someOtherService;
}

我现在遇到了使用另一种约定来实现相同目标的代码

@Component
public class SomeService {
    private final SomeOtherService someOtherService;

    @Autowired
    public SomeService(SomeOtherService someOtherService){
        this.someOtherService = someOtherService;
    }
}

我知道这两种方法都有效。但是选择B有什么好处吗?对我来说，它在类和单元测试中创建了更多的代码。(必须写构造函数，不能使用@InjectMocks)

我遗漏了什么吗?除了将代码添加到单元测试之外，自动连接构造函数还有其他功能吗?这是一种更可取的依赖注入方式吗?

假设我有两个c++类:

class A
{
public:
  A() { fn(); }

  virtual void fn() { _n = 1; }
  int getn() { return _n; }

protected:
  int _n;
};

class B : public A
{
public:
  B() : A() {}

  virtual void fn() { _n = 2; }
};

如果我写下面的代码:

int main()
{
  B b;
  int n = b.getn();
}

有人可能认为n被设为2。

结果是n被设为1。为什么?

除了名字以外，这些类之间有什么不同吗?

class WithClass ():
    def __init__(self):
        self.value = "Bob"
    def my_func(self):
        print(self.value)

class WithoutClass ():
    value = "Bob"

    def my_func(self):
        print(self.value)

如果我使用或不使用__init__方法来声明变量值，会有任何区别吗?

我主要担心的是，我只会以一种方式使用它，而这会给我带来更多的问题。

为什么这个代码:

class A
{
    public: 
        explicit A(int x) {}
};

class B: public A
{
};

int main(void)
{
    B *b = new B(5);
    delete b;
}

导致以下错误:

main.cpp: In function ‘int main()’:
main.cpp:13: error: no matching function for call to ‘B::B(int)’
main.cpp:8: note: candidates are: B::B()
main.cpp:8: note:                 B::B(const B&)

B不应该继承A的构造函数吗?

(这是使用gcc)

这是我的错误:

(mysite)zjm1126@zjm1126-G41MT-S2:~/zjm_test/mysite$ pip install lxml
Downloading/unpacking lxml
  Running setup.py egg_info for package lxml
    Building lxml version 2.3.
    Building without Cython.
    ERROR: /bin/sh: xslt-config: not found

    ** make sure the development packages of libxml2 and libxslt are installed **

    Using build configuration of libxslt
Installing collected packages: lxml
  Running setup.py install for lxml
    Building lxml version 2.3.
    Building without Cython.
    ERROR: /bin/sh: xslt-config: not found

    ** make sure the development packages of libxml2 and libxslt are installed **

    Using build configuration of libxslt
    building 'lxml.etree' extension
    gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fPIC -I/usr/include/python2.6 -c src/lxml/lxml.etree.c -o build/temp.linux-i686-2.6/src/lxml/lxml.etree.o -w
    src/lxml/lxml.etree.c:4: fatal error: Python.h: 没有那个文件或目录
    compilation terminated.
    error: command 'gcc' failed with exit status 1
    Complete output from command /home/zjm1126/zjm_test/mysite/bin/python -c "import setuptools;__file__='/home/zjm1126/zjm_test/mysite/build/lxml/setup.py';execfile(__file__)" install --single-version-externally-managed --record /tmp/pip-jOhgvD-record/install-record.txt --install-headers /home/zjm1126/zjm_test/mysite/include/site/python2.6:
    Building lxml version 2.3.

Building without Cython.

ERROR: /bin/sh: xslt-config: not found



** make sure the development packages of libxml2 and libxslt are installed **



Using build configuration of libxslt

running install

running build

running build_py

running build_ext

building 'lxml.etree' extension

gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fPIC -I/usr/include/python2.6 -c src/lxml/lxml.etree.c -o build/temp.linux-i686-2.6/src/lxml/lxml.etree.o -w

src/lxml/lxml.etree.c:4: fatal error: Python.h: 没有那个文件或目录

compilation terminated.

error: command 'gcc' failed with exit status 1

----------------------------------------
Command /home/zjm1126/zjm_test/mysite/bin/python -c "import setuptools;__file__='/home/zjm1126/zjm_test/mysite/build/lxml/setup.py';execfile(__file__)" install --single-version-externally-managed --record /tmp/pip-jOhgvD-record/install-record.txt --install-headers /home/zjm1126/zjm_test/mysite/include/site/python2.6 failed with error code 1
Storing complete log in /home/zjm1126/.pip/pip.log

我该怎么办?

更新:

(mysite)zjm1126@zjm1126-G41MT-S2:~/zjm_test/mysite$ pip install lxml
Downloading/unpacking lxml
  Running setup.py egg_info for package lxml
    Building lxml version 2.3.
    Building without Cython.
    Using build configuration of libxslt 1.1.26
    Building against libxml2/libxslt in the following directory: /usr/lib
Installing collected packages: lxml
  Running setup.py install for lxml
    Building lxml version 2.3.
    Building without Cython.
    Using build configuration of libxslt 1.1.26
    Building against libxml2/libxslt in the following directory: /usr/lib
    building 'lxml.etree' extension
    gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fPIC -I/usr/include/libxml2 -I/usr/include/python2.6 -c src/lxml/lxml.etree.c -o build/temp.linux-i686-2.6/src/lxml/lxml.etree.o -w
    src/lxml/lxml.etree.c:4: fatal error: Python.h: 没有那个文件或目录
    compilation terminated.
    error: command 'gcc' failed with exit status 1
    Complete output from command /home/zjm1126/zjm_test/mysite/bin/python -c "import setuptools;__file__='/home/zjm1126/zjm_test/mysite/build/lxml/setup.py';execfile(__file__)" install --single-version-externally-managed --record /tmp/pip-NJw2ws-record/install-record.txt --install-headers /home/zjm1126/zjm_test/mysite/include/site/python2.6:
    Building lxml version 2.3.

Building without Cython.

Using build configuration of libxslt 1.1.26

Building against libxml2/libxslt in the following directory: /usr/lib

running install

running build

running build_py

running build_ext

building 'lxml.etree' extension

gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fPIC -I/usr/include/libxml2 -I/usr/include/python2.6 -c src/lxml/lxml.etree.c -o build/temp.linux-i686-2.6/src/lxml/lxml.etree.o -w

src/lxml/lxml.etree.c:4: fatal error: Python.h: 没有那个文件或目录

compilation terminated.

error: command 'gcc' failed with exit status 1

----------------------------------------
Command /home/zjm1126/zjm_test/mysite/bin/python -c "import setuptools;__file__='/home/zjm1126/zjm_test/mysite/build/lxml/setup.py';execfile(__file__)" install --single-version-externally-managed --record /tmp/pip-NJw2ws-record/install-record.txt --install-headers /home/zjm1126/zjm_test/mysite/include/site/python2.6 failed with error code 1
Storing complete log in /home/zjm1126/.pip/pip.log

日志:

------------------------------------------------------------
/home/zjm1126/zjm_test/mysite/bin/pip run on Thu Mar  3 17:07:27 2011
Downloading/unpacking mysql-python
  Running setup.py egg_info for package mysql-python
    running egg_info
    creating pip-egg-info/MySQL_python.egg-info
    writing pip-egg-info/MySQL_python.egg-info/PKG-INFO
    writing top-level names to pip-egg-info/MySQL_python.egg-info/top_level.txt
    writing dependency_links to pip-egg-info/MySQL_python.egg-info/dependency_links.txt
    writing pip-egg-info/MySQL_python.egg-info/PKG-INFO
    writing top-level names to pip-egg-info/MySQL_python.egg-info/top_level.txt
    writing dependency_links to pip-egg-info/MySQL_python.egg-info/dependency_links.txt
    writing manifest file 'pip-egg-info/MySQL_python.egg-info/SOURCES.txt'
    warning: manifest_maker: standard file '-c' not found
    reading manifest file 'pip-egg-info/MySQL_python.egg-info/SOURCES.txt'
    reading manifest template 'MANIFEST.in'
    warning: no files found matching 'MANIFEST'
    warning: no files found matching 'ChangeLog'
    warning: no files found matching 'GPL'
    writing manifest file 'pip-egg-info/MySQL_python.egg-info/SOURCES.txt'
Installing collected packages: mysql-python
  Running setup.py install for mysql-python
    Running command /home/zjm1126/zjm_test/mysite/bin/python -c "import setuptools;__file__='/home/zjm1126/zjm_test/mysite/build/mysql-python/setup.py';execfile(__file__)" install --single-version-externally-managed --record /tmp/pip-XuVIux-record/install-record.txt --install-headers /home/zjm1126/zjm_test/mysite/include/site/python2.6
    running install
    running build
    running build_py
    creating build
    creating build/lib.linux-i686-2.6
    copying _mysql_exceptions.py -> build/lib.linux-i686-2.6
    creating build/lib.linux-i686-2.6/MySQLdb
    copying MySQLdb/__init__.py -> build/lib.linux-i686-2.6/MySQLdb
    copying MySQLdb/converters.py -> build/lib.linux-i686-2.6/MySQLdb
    copying MySQLdb/connections.py -> build/lib.linux-i686-2.6/MySQLdb
    copying MySQLdb/cursors.py -> build/lib.linux-i686-2.6/MySQLdb
    copying MySQLdb/release.py -> build/lib.linux-i686-2.6/MySQLdb
    copying MySQLdb/times.py -> build/lib.linux-i686-2.6/MySQLdb
    creating build/lib.linux-i686-2.6/MySQLdb/constants
    copying MySQLdb/constants/__init__.py -> build/lib.linux-i686-2.6/MySQLdb/constants
    copying MySQLdb/constants/CR.py -> build/lib.linux-i686-2.6/MySQLdb/constants
    copying MySQLdb/constants/FIELD_TYPE.py -> build/lib.linux-i686-2.6/MySQLdb/constants
    copying MySQLdb/constants/ER.py -> build/lib.linux-i686-2.6/MySQLdb/constants
    copying MySQLdb/constants/FLAG.py -> build/lib.linux-i686-2.6/MySQLdb/constants
    copying MySQLdb/constants/REFRESH.py -> build/lib.linux-i686-2.6/MySQLdb/constants
    copying MySQLdb/constants/CLIENT.py -> build/lib.linux-i686-2.6/MySQLdb/constants
    running build_ext
    building '_mysql' extension
    creating build/temp.linux-i686-2.6
    gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fPIC -Dversion_info=(1,2,3,'final',0) -D__version__=1.2.3 -I/usr/include/mysql -I/usr/include/python2.6 -c _mysql.c -o build/temp.linux-i686-2.6/_mysql.o -DBIG_JOINS=1 -fno-strict-aliasing -DUNIV_LINUX -DUNIV_LINUX
    In file included from _mysql.c:29:
    pymemcompat.h:10: fatal error: Python.h: 没有那个文件或目录
    compilation terminated.
    error: command 'gcc' failed with exit status 1
    Complete output from command /home/zjm1126/zjm_test/mysite/bin/python -c "import setuptools;__file__='/home/zjm1126/zjm_test/mysite/build/mysql-python/setup.py';execfile(__file__)" install --single-version-externally-managed --record /tmp/pip-XuVIux-record/install-record.txt --install-headers /home/zjm1126/zjm_test/mysite/include/site/python2.6:
    running install

running build

running build_py

creating build

creating build/lib.linux-i686-2.6

copying _mysql_exceptions.py -> build/lib.linux-i686-2.6

creating build/lib.linux-i686-2.6/MySQLdb

copying MySQLdb/__init__.py -> build/lib.linux-i686-2.6/MySQLdb

copying MySQLdb/converters.py -> build/lib.linux-i686-2.6/MySQLdb

copying MySQLdb/connections.py -> build/lib.linux-i686-2.6/MySQLdb

copying MySQLdb/cursors.py -> build/lib.linux-i686-2.6/MySQLdb

copying MySQLdb/release.py -> build/lib.linux-i686-2.6/MySQLdb

copying MySQLdb/times.py -> build/lib.linux-i686-2.6/MySQLdb

creating build/lib.linux-i686-2.6/MySQLdb/constants

copying MySQLdb/constants/__init__.py -> build/lib.linux-i686-2.6/MySQLdb/constants

copying MySQLdb/constants/CR.py -> build/lib.linux-i686-2.6/MySQLdb/constants

copying MySQLdb/constants/FIELD_TYPE.py -> build/lib.linux-i686-2.6/MySQLdb/constants

copying MySQLdb/constants/ER.py -> build/lib.linux-i686-2.6/MySQLdb/constants

copying MySQLdb/constants/FLAG.py -> build/lib.linux-i686-2.6/MySQLdb/constants

copying MySQLdb/constants/REFRESH.py -> build/lib.linux-i686-2.6/MySQLdb/constants

copying MySQLdb/constants/CLIENT.py -> build/lib.linux-i686-2.6/MySQLdb/constants

running build_ext

building '_mysql' extension

creating build/temp.linux-i686-2.6

gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fPIC -Dversion_info=(1,2,3,'final',0) -D__version__=1.2.3 -I/usr/include/mysql -I/usr/include/python2.6 -c _mysql.c -o build/temp.linux-i686-2.6/_mysql.o -DBIG_JOINS=1 -fno-strict-aliasing -DUNIV_LINUX -DUNIV_LINUX

In file included from _mysql.c:29:

pymemcompat.h:10: fatal error: Python.h: 没有那个文件或目录

compilation terminated.

error: command 'gcc' failed with exit status 1

----------------------------------------
Command /home/zjm1126/zjm_test/mysite/bin/python -c "import setuptools;__file__='/home/zjm1126/zjm_test/mysite/build/mysql-python/setup.py';execfile(__file__)" install --single-version-externally-managed --record /tmp/pip-XuVIux-record/install-record.txt --install-headers /home/zjm1126/zjm_test/mysite/include/site/python2.6 failed with error code 1
Exception information:
Traceback (most recent call last):
  File "/home/zjm1126/zjm_test/mysite/lib/python2.6/site-packages/pip-0.8.1-py2.6.egg/pip/basecommand.py", line 130, in main
    self.run(options, args)
  File "/home/zjm1126/zjm_test/mysite/lib/python2.6/site-packages/pip-0.8.1-py2.6.egg/pip/commands/install.py", line 228, in run
    requirement_set.install(install_options, global_options)
  File "/home/zjm1126/zjm_test/mysite/lib/python2.6/site-packages/pip-0.8.1-py2.6.egg/pip/req.py", line 1043, in install
    requirement.install(install_options, global_options)
  File "/home/zjm1126/zjm_test/mysite/lib/python2.6/site-packages/pip-0.8.1-py2.6.egg/pip/req.py", line 559, in install
    cwd=self.source_dir, filter_stdout=self._filter_install, show_stdout=False)
  File "/home/zjm1126/zjm_test/mysite/lib/python2.6/site-packages/pip-0.8.1-py2.6.egg/pip/__init__.py", line 249, in call_subprocess
    % (command_desc, proc.returncode))
InstallationError: Command /home/zjm1126/zjm_test/mysite/bin/python -c "import setuptools;__file__='/home/zjm1126/zjm_test/mysite/build/mysql-python/setup.py';execfile(__file__)" install --single-version-externally-managed --record /tmp/pip-XuVIux-record/install-record.txt --install-headers /home/zjm1126/zjm_test/mysite/include/site/python2.6 failed with error code 1

我想设置我的本地开发机器，以便任何对*的请求。Local被重定向到localhost。这个想法是，当我开发多个站点时，我只需向Apache添加名为site1的vhosts。地方,site2。让它们都解析到localhost，而Apache则相应地服务于不同的站点。

我用的是Windows XP。

我试着加上

127.0.0.1       *.local

到我的c:\windows\system32\drivers\etc\hosts文件，也试过:

127.0.0.1       .local

这两种方法似乎都不管用。

我知道我可以在不同的端口号上设置它们，但这是一种痛苦，因为很难记住哪个端口是哪个端口。

我不想设置本地DNS服务器，有什么建议吗?

如何查看Debian机器上安装了Apache的哪个版本?

有这样做的命令吗?

我正在与一位同事讨论从构造函数抛出异常的问题，我想我需要一些反馈。

从设计的角度来看，从构造函数抛出异常是否正确?

假设我在一个类中包装了一个POSIX互斥锁，它看起来像这样:

class Mutex {
public:
  Mutex() {
    if (pthread_mutex_init(&mutex_, 0) != 0) {
      throw MutexInitException();
    }
  }

  ~Mutex() {
    pthread_mutex_destroy(&mutex_);
  }

  void lock() {
    if (pthread_mutex_lock(&mutex_) != 0) {
      throw MutexLockException();
    }
  }

  void unlock() {
    if (pthread_mutex_unlock(&mutex_) != 0) {
      throw MutexUnlockException();
    }
  }

private:
  pthread_mutex_t mutex_;
};

我的问题是，这是标准的方法吗?因为如果pthread mutex_init调用失败，互斥锁对象将不可用，因此抛出异常将确保不会创建互斥锁。

我是否应该为Mutex类创建一个成员函数init，并调用pthread mutex_init，其中将返回基于pthread mutex_init的返回的bool值?这样我就不必为如此低级的对象使用异常了。

当我试图运行我的应用程序内计费我得到的错误:“这个版本的应用程序没有配置通过谷歌播放计费。查看帮助中心获取更多信息”。

我已经在Manifest文件中有计费权限，我有一个签名的。apk作为草稿上传到谷歌Play上，我也已经在我的手机上安装了相同的签名apk。

有什么帮助可以解决这个问题吗?