Python| os.getenv() 方法

Python中的OS 模块提供了与操作系统交互的功能。操作系统属于 Python 的标准实用程序模块。该模块提供了一种使用操作系统相关功能的可移植方式。

Python中的os.getenv()方法返回环境变量键的值（如果存在），否则返回默认值。

Syntax: os.getenv(key, default = None)

Parameters:
key: string denoting the name of environment variable
default (optional) : string denoting the default value in case key does not exists. If omitted default is set to ‘None’.

Return Type: This method returns a string that denotes the value of the environment variable key. In case key does not exists it returns the value of default parameter.

代码 #1：使用 os.getenv() 方法

# Python program to explain os.getenv() method 
    
# importing os module 
import os
  
# Get the value of 'HOME'
# environment variable
key = 'HOME'
value = os.getenv(key)
  
# Print the value of 'HOME'
# environment variable
print("Value of 'HOME' environment variable :", value) 
  
# Get the value of 'JAVA_HOME'
# environment variable
key = 'JAVA_HOME'
value = os.getenv(key)
  
# Print the value of 'JAVA_HOME'
# environment variable
print("Value of 'JAVA_HOME' environment variable :", value) 

输出：

Value of 'HOME' environment variable : /home/ihritik
Value of 'JAVA_HOME' environment variable : /opt/jdk-10.0.1

代码#2：如果键不存在

# Python program to explain os.getenv() method 
    
# importing os module 
import os
  
# Get the value of 'home'
# environment variable
key = 'home'
value = os.getenv(key)
  
# Print the value of 'home'
# environment variable
print("Value of 'home' environment variable :", value)

输出：

Value of 'home' environment variable : None

代码 #3：显式指定默认参数

# Python program to explain os.getenv() method 
    
# importing os module 
import os
  
# Get the value of 'home'
# environment variable
key = 'home'
value = os.getenv(key, "value does not exist")
  
# Print the value of 'home'
# environment variable
print("Value of 'home' environment variable :", value) 

输出：

Value of 'home' environment variable : value does not exist