What does import in python mean?

#The import statement in Python is used to call modules.

1. Module

Usually the module is a file, just use import to import it directly. The file types that can be used as modules include ".py", ".pyo", ".pyc", ".pyd", ".so", and ".dll".

2. Package

Usually a package is always a directory. You can use import to import the package, or from import to import some modules in the package. The first file in the package directory is __init__.py. Then there are some module files and subdirectories. If there is also __init__.py in the subdirectory, then it is a subpackage of this package.

Module

You can use the import statement to import a source code file as a module. For example:

# file : spam.py
a = 37                    # 一个变量
def foo:                  # 一个函数
    print "I'm foo"
class bar:                # 一个类
    def grok(self):
        print "I'm bar.grok"
b = bar()                 # 创建一个实例

Use the import spam statement to import this file as a module. When the system imports a module, it must do the following three things:
1. Create a namespace for the objects defined in the source code file. Through this namespace, you can access the functions and variables defined in the module.

2. Execute the source code file in the newly created namespace.

3. Create an object named the source code file, which references the module’s namespace, so that it can be executed through This object accesses functions and variables in the module, such as:

 import spam           # 导入并运行模块 spam
 print spam.a          # 访问模块 spam 的属性
 spam.foo()
 c = spam.bar()
 ...

Use commas to separate the module names to import multiple modules at the same time:
import socket, os, regex modules can be imported using the as keyword. Change the name of the reference object of the module:

import os as system
import socket as net, thread as threads
system.chdir("..")
net.gethostname()

Use the from statement to directly import the objects in the module into the current name space. The from statement does not create a reference object to the module name space, but imports the imported module One or more objects are directly placed into the current namespace:

from socket import gethostname
                               # 将gethostname放如当前名字空间
print gethostname()            # 直接调用
socket.gethostname()           # 引发异常NameError: socket

The from statement supports comma-separated objects, and an asterisk (*) can also be used to represent all objects in the module except those starting with an underscore:

from socket import gethostname, socket
from socket import *   # 载入所有对象到当前名字空间

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