让 python 脚本检查丢失的模块并在丢失时安装

Question

我正在寻求使我编写的脚本更便携。

我的脚本中使用的一些工具需要安装某些模块。我已经能够让脚本自行安装模块，但希望有一种机制来检查它们是否已经安装，并且只有在缺失时才尝试安装。

我确信这是可能的，但我似乎找不到解决方案。

Answer 1

你可以试试这个：

import pip
def install(package):
    pip.main(['install', package])

try:
    import your_module
except ImportError:
    print 'Module not installed'
    install('your_module')

Answer 2

解决这个问题的标准方法是把你的脚本变成一个模块，declare its dependencies in the setup.py of the module.

from setuptools import setup

setup(name='foo',
  ...
  install_requires=['dependency', 'other', ...])

支持性较弱的约定是在requirements.txt 中保留一个列表，以便您可以

pip install -r requirements.txt

让你自己的脚本来做这些家务通常没有用也没有必要；现有的打包基础设施已经提供了你需要的东西，并且是操作和管理包依赖关系的自然点。

从历史上看，随着不同的封装机制在 Python 生态系统中争夺主导地位，曾出现过一些动荡，但现在看来，setuptools 和 pip 已基本确定。

Answer 3

通常，代表运行您的脚本的人下载和安装东西并不好。正如 Triplee 的回答所提到的，使用 requirements.txt 和适当的 setup.py 是一种标准且更好的做法。

无论如何，以下是在脚本中获得所需行为的技巧。

import pip
import importlib
modules = ['requests', 'fake_module_name_that_does_not_exist']
for modname in modules:
    try:
        # try to import the module normally and put it in globals
        globals()[modname] = importlib.import_module(modname)
    except ImportError as e:
        result = pip.main(['install', modname])
        if result != 0: # if pip could not install it reraise the error
            raise
        else:
            # if the install was sucessful, put modname in globals
            globals()[modname] = importlib.import_module(modname)

如果你要执行这个例子，你会得到如下输出

Collecting requests
  Using cached requests-2.18.4-py2.py3-none-any.whl
Requirement already satisfied: idna<2.7,>=2.5 in c:\users\spenceryoung\envs\test_venv\lib\site-packages (from requests)
Requirement already satisfied: urllib3<1.23,>=1.21.1 in c:\users\spenceryoung\envs\test_venv\lib\site-packages (from requests)
Requirement already satisfied: chardet<3.1.0,>=3.0.2 in c:\users\spenceryoung\envs\test_venv\lib\site-packages (from requests)
Requirement already satisfied: certifi>=2017.4.17 in c:\users\spenceryoung\envs\test_venv\lib\site-packages (from requests)
Installing collected packages: requests
Successfully installed requests-2.18.4
Collecting fake_module_name_that_does_not_exist
  Could not find a version that satisfies the requirement fake_module_name_that_does_not_exist (from versions: )
No matching distribution found for fake_module_name_that_does_not_exist
Traceback (most recent call last):
  File "<stdin>", line 3, in <module>
  File "C:\Users\spenceryoung\AppData\Local\Programs\Python\Python36-32\lib\importlib\__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 994, in _gcd_import
  File "<frozen importlib._bootstrap>", line 971, in _find_and_load
  File "<frozen importlib._bootstrap>", line 953, in _find_and_load_unlocked
ModuleNotFoundError: No module named 'fake_module_name_that_does_not_exist'