python os.environ()和os.getenv()方区别

 os.environ() 如果环境变量不存在，则引发异常。

 os.getenv() 不引发异常，但返回None。os.getenv()  读取环境变量。比如，os.getenv('PATH')

Python | os.environ object

 

• Difficulty Level : Easy
• Last Updated : 13 Apr, 2022

OS module in Python provides functions for interacting with the operating system. OS comes under Python’s standard utility modules. This module provides a portable way of using operating system dependent functionality.

os.environ in Python is a mapping object that represents the user’s environmental variables. It returns a dictionary having user’s environmental variable as key and their values as value.

os.environ behaves like a python dictionary, so all the common dictionary operations like get and set can be performed. We can also modify os.environ but any changes will be effective only for the current process where it was assigned and it will not change the value permanently.

 

Syntax: os.environ

Parameter: It is a non-callable object. Hence, no parameter is required

Return Type: This returns a dictionary representing the user’s environmental variables

Code #1: Use of os.environ to get access of environment variables

 

# Python program to explain os.environ object 

  

# importing os module 

import os

import pprint

  

# Get the list of user's

# environment variables

env_var = os.environ

  

# Print the list of user's

# environment variables

print("User's Environment variable:")

pprint.pprint(dict(env_var), width = 1)

Output:

{'CLUTTER_IM_MODULE': 'xim',
 'COLORTERM': 'truecolor',
 'DBUS_SESSION_BUS_ADDRESS': 'unix:path=/run/user/1000/bus',
 'DESKTOP_SESSION': 'ubuntu',
 'DISPLAY': ':0',
 'GDMSESSION': 'ubuntu',
 'GJS_DEBUG_OUTPUT': 'stderr',
 'GJS_DEBUG_TOPICS': 'JS '
                     'ERROR;JS '
                     'LOG',
 'GNOME_DESKTOP_SESSION_ID': 'this-is-deprecated',
 'GNOME_SHELL_SESSION_MODE': 'ubuntu',
 'GTK_IM_MODULE': 'ibus',
 'HOME': '/home/ihritik',
 'IM_CONFIG_PHASE': '2',
 'JAVA_HOME': '/opt/jdk-10.0.1',
 'JOURNAL_STREAM': '9:28586',
 'JRE_HOME': '/opt/jdk-10.0.1/jre',
 'LANG': 'en_IN',
 'LANGUAGE': 'en_IN:en',
 'LESSCLOSE': '/usr/bin/lesspipe '
              '%s '
              '%s',
 'LESSOPEN': '| '
             '/usr/bin/lesspipe '
             '%s',
 'LOGNAME': 'ihritik',
 'PATH': '/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:
/usr/local/games:/snap/bin:/usr/local/java/jdk-10.0.1/bin:
/usr/local/java/jdk-10.0.1/jre/bin:/opt/jdk-10.0.1/bin:/opt/jdk-10.0.1/jre/bin',
 'PWD': '/home/ihritik',
 'QT4_IM_MODULE': 'xim',
 'QT_IM_MODULE': 'ibus',
 'SESSION_MANAGER': 'local/hritik:@/tmp/.ICE-unix/1127, unix/hritik:/tmp/.ICE-unix/1127',
 'SHELL': '/bin/bash',
 'SHLVL': '2',
 'SSH_AUTH_SOCK': '/run/user/1000/keyring/ssh',
 'TERM': 'xterm-256color',
 'TEXTDOMAIN': 'im-config',
 'TEXTDOMAINDIR': '/usr/share/locale/',
 'USER': 'ihritik',
 'USERNAME': 'ihritik',
 'VTE_VERSION': '4804',
 'WAYLAND_DISPLAY': 'wayland-0',
 'XDG_CONFIG_DIRS': '/etc/xdg/xdg-ubuntu:/etc/xdg',
 'XDG_CURRENT_DESKTOP': 'ubuntu:GNOME',
 'XDG_MENU_PREFIX': 'gnome-',
 'XDG_RUNTIME_DIR': '/run/user/1000',
 'XDG_SEAT': 'seat0',
 'XDG_SESSION_DESKTOP': 'ubuntu',
 'XDG_SESSION_ID': '2',
 'XDG_SESSION_TYPE': 'wayland',
 'XDG_VTNR': '2',
 'XMODIFIERS': '@im=ibus',
 '_': '/usr/bin/python3'}

Code #2: Accessing a particular environment variable

 

# Python program to explain os.environ object 

  

# importing os module 

import os

  

# Get the value of

# 'HOME' environment variable

home = os.environ['HOME']

  

# Print the value of

# 'HOME' environment variable

print("HOME:", home)

  

# Get the value of

# 'JAVA_HOME' environment variable

# using get operation of dictionary

java_home = os.environ.get('JAVA_HOME')

  

# Print the value of

# 'JAVA_HOME' environment variable

print("JAVA_HOME:", java_home)

Output:

HOME: /home/ihritik
JAVA_HOME: /opt/jdk-10.0.1

Code #3: Modifying a environment variable

 

# Python program to explain os.environ object 

  

# importing os module 

import os

  

  

# Print the value of

# 'JAVA_HOME'  environment variable 

print("JAVA_HOME:", os.environ['JAVA_HOME'])

  

# Modify the value of

# 'JAVA_HOME'  environment variable 

os.environ['JAVA_HOME'] = '/home / ihritik / jdk-10.0.1'

  

# Print the modified value of

# 'JAVA_HOME' environment variable

print("Modified JAVA_HOME:", os.environ['JAVA_HOME'])

Output:

JAVA_HOME: /opt/jdk-10.0.1
Modified JAVA_HOME: /home/ihritik/jdk-10.0.1

Code #4: Adding a new environment variable

 

# Python program to explain os.environ object 

  

# importing os module 

import os

  

# Add a new environment variable 

os.environ['GeeksForGeeks'] = 'www.geeksforgeeks.org'

  

# Get the value of

# Added environment variable 

print("GeeksForGeeks:", os.environ['GeeksForGeeks'])

Output:

GeeksForGeeks: www.geeksforgeeks.org

Code #5: Accessing a environment variable which does not exists

 

# Python program to explain os.environ object 

  

# importing os module 

import os

  

# Print the value of

# 'MY_HOME' environment variable 

print("MY_HOME:", os.environ['MY_HOME']

  

  

# If the key does not exists

# it will produce an error

Output:

Traceback (most recent call last):
  File "osenviron.py", line 8, in 
    print("MY_HOME:", os.environ['MY_HOME'])
  File "/usr/lib/python3.6/os.py", line 669, in __getitem__
    raise KeyError(key) from None
KeyError: 'MY_HOME'

Code #6: Handling error while Accessing a environment variable which does not exists

 

# Python program to explain os.environ object 

  

  

# importing os module 

import os

  

# Method 1

# Print the value of

# 'MY_HOME' environment variable 

print("MY_HOME:", os.environ.get('MY_HOME', "Environment variable does not exist"))

  

  

# Method 2

try:

    print("MY_HOME:", os.environ['MY_HOME'])

except KeyError: 

    print("Environment variable does not exist")

Output:

MY_HOME: Environment variable does not exist
Environment variable does not exist

Python | os.getenv() method

 

• Difficulty Level : Easy
• Last Updated : 20 May, 2019

OS module in Python provides functions for interacting with the operating system. OS comes under Python’s standard utility modules. This module provides a portable way of using operating system dependent functionality.

os.getenv() method in Python returns the value of the environment variable key if it exists otherwise returns the default value.

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.

Code #1: use of os.getenv() method

 

# 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) 

Output:

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

 

Code #2: if key does not exist

 

# 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)

Output:

Value of 'home' environment variable : None

 

Code #3: Explicitly specifying default parameter

 

# 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) 

Output:

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