Python os.getenv()

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

语法:os.getenv(key, default = None)

参数:

key:表示环境变量名的字符串

Default(可选):字符串，表示key不存在时的默认值。如果省略，默认设置为“None”。

返回类型:该方法返回一个字符串，表示环境变量key的值。如果key不存在，则返回默认参数的值。

示例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

示例2

如果key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

示例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