如何读取 Windows 环境变量值?

问题描述

我试过了:

os.environ['MyVar']

但它没有用！有没有适合所有操作系统的方法?

But it did not work! Is there any way suitable for all operating systems?

推荐答案

尝试使用以下方法:

os.getenv('MyVar')

来自文档:

os.getenv(varname[, value])

os.getenv(varname[, value])

如果存在则返回环境变量 varname 的值，如果不存在则返回值.值默认为无.

Return the value of the environment variable varname if it exists, or value if it doesn’t. value defaults to None.

可用性:大多数版本的 Unix、Windows

Availability: most flavors of Unix, Windows

所以在测试之后:

>>> import os
>>> os.environ['MyVar'] = 'Hello World!'       # set the environment variable 'MyVar' to contain 'Hello World!'
>>> print os.getenv('MyVar')
Hello World!
>>> print os.getenv('not_existing_variable')
None
>>> print os.getenv('not_existing_variable', 'that variable does not exist')
that variable does not exist
>>> print os.environ['MyVar']
Hello World!
>>> print os.environ['not_existing_variable']
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "/usr/lib/python2.4/UserDict.py", line 17, in __getitem__
    def __getitem__(self, key): return self.data[key]
KeyError: 'not_existing_variable    

如果环境变量存在，您的方法也可以工作.使用 os.getenv 的区别在于它返回 None (或给定的值)，而 os.environ['MyValue'] 给出变量不存在时发生 KeyError 异常.

Your method would work too if the environmental variable exists. The difference with using os.getenv is that it returns None (or the given value), while os.environ['MyValue'] gives a KeyError exception when the variable does not exist.

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