使用`python -m pip'而不是只是`pip'有什么影响？
当我使用 python -m pip install＆lt; package＆gt; 时，这与仅使用 pip install＆lt; package＆gt; 有何不同？同样，为什么我要编写 python -m pip install -upgrade pip 升级pip，而不是 pip install -upgrade -upgrade pip ？
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考虑以下情况。
您安装了三个版本的Python：
您的“默认”版本为3.8。这是出现在您的路径中的第一个。因此，当您键入
python3（linux或mac）或python（windows）在shell中，您将启动3.8解释器，因为这是第一个在穿越时发现的python可执行文件你的道路。假设您正在启动一个新项目，您要在其中使用Python 3.9。您创建一个称为
.venv的虚拟环境并激活它。现在，我们使用Python 3.9激活了虚拟环境。在外壳中键入
python启动了3.9解释器。但是，如果您键入
，则使用哪种版本的
pip？是默认版本的PIP，即Python 3.8还是虚拟环境中的Python版本？解决这种歧义的一种简单方法是仅使用
-M标志，确保您使用与活动python可执行的pip。即使您只安装了一个全局版本的Python，也可以始终使用
-M，这是一个很好的做法。关于。路径
所谓的路径是您的系统搜索可执行文件的目录列表。当您键入命令（例如
python）时，此列表将从第一个目录到最后一个目录，搜索与您键入的命令匹配的文件名。如果找到文件名/命令，则匹配的文件将执行，而无需考虑潜在的以后匹配。如果没有发生匹配，则找不到
命令或其变体。这种行为是设计的。在UNIX系统上，路径环境变量被称为
$ path，而在Windows系统上，它被称为％path％更多有关
-m -flag（2022年12月）大多数查看此问题的人可能希望上面用PIP给出的解释。不过，从更一般的意义上讲，当使用
python -m some_module时，-mflag使Python Executesome_module作为脚本。这在“以脚本运行”是什么意思
？在导入文件的顶部语句。这可以使用
some_module在导入文件中定义的函数，类和变量。要执行
some_module作为脚本而不是导入它，如果__name__ ==“ __ -main __” block在文件中，您将定义。在命令行上运行python some_module.py时，该块将执行。这很有用，因为您 不希望此代码块在导入其他文件时运行，但是您 do 希望它在从命令行调用时运行。对于项目中的模块，此脚本/模块构造应按原样运行，因为从终端运行时，Python会从您的工作目录中找到模块：
但是对于Python标准库的一个模块，这将行不通。 Python文档中的示例使用
timeIt（pip工作相同）：这返回错误：
“ Python：coble file'/home/＆lt ;用户名＆gt;/timeit'：[errno 2]否此类文件或目录“添加
-mflag告诉Python告诉Python，请在timeit.py.py的路径中寻找路径并执行如果__name__ ==“ __ -main __”从文件中的子句。这是预期的。
的来源如果__name __ ==“ __ main __”可以找到时间级模块的块此处。Consider the following scenario.
You have three versions of Python installed:
Your "default" version is 3.8. It's the first one appearing in your path. Therefore, when you type
python3(Linux or Mac) orpython(Windows) in a shell you will start a 3.8 interpreter because that's the first Python executable that is found when traversing your path.Suppose you are then starting a new project where you want to use Python 3.9. You create a virtual environment called
.venvand activate it.We now have the virtual environment activated using Python 3.9. Typing
pythonin a shell starts the 3.9 interpreter.BUT, if you type
Then what version of
pipis used? Is it the pip for the default version, i.e. Python 3.8, or the Python version within the virtual environment?An easy way to get around that ambiguity is simply to use
The
-mflag makes sure that you are using the pip that's tied to the active Python executable.It's good practice to always use
-m, even if you have just one global version of Python installed from which you create virtual environments.Re. path
The so-called path is a list of directories where your system searches for executables. When you type a command, like
python, this list is traversed from the first directory to the last, searching for a filename that matches the command you typed.If the filename/command is found, the matched file gets executed without taking into account potential later matches. If no match occurs, you get a
Command not foundor a variation thereof. This behavior is by design.On UNIX systems the path environment variable is called
$PATH, while on Windows systems it's referred to as%PATH%More general comments about the
-m-flag (Dec. 2022)Most people viewing this will likely want the explanation given above with pip. In a more general sense though, when using
python -m some_module, the-mflag makes Python executesome_moduleas a script. This is stated in the docs, but might be difficult to understand without some baseline knowledge.What does it mean to "run as a script"?
In Python, a module
some_moduleis typically imported into another Python file with animport some_modulestatement at the top of the importing file. This enables the use of functions, classes, and variables defined insome_moduleinside the importing file.To execute
some_moduleas a script instead of importing it, you would define anif __name__ == "__main__"block inside the file. This block gets executed when runningpython some_module.pyon the command line. This is useful because you do not want this code block to run when importing into other files, but you do want it to run when invoked from the command line.For modules inside your project, this script/module construct should run as is, because Python will find the module from your working directory when running from the terminal:
But for modules that are part of Python's Standard Library, this will not work. The example from the Python docs uses
timeit(pipworks the same):This returns the error:
"python: can't open file '/home/<username>/timeit': [Errno 2] No such file or directory"Adding the
-mflag tells Python to look in path fortimeit.pyand execute theif __name__ == "__main__"clause from the file.This works as expected.
The source for the
if __name__ == "__main__"block for the timeit module can be found here.来自 python docs ：
From Python Docs:
键入
python - -help，如果您
如果您使用
命令-help或man命令If you type
python --helpYou get
A great many things in a terminal will show you how to use it if you either use
command --helporman command-m代表模块名称。来自命令行和环境：
The
-mstands formodule-name.From Command line and environment:
当
-m与命令行上的python语句一起使用时，然后是＆lt; module_name＆gt;，然后使模块成为作为可执行文件执行。您可以参考相同的python文档，也可以运行
python -helpWhen
-mis used with apythonstatement on the command line, followed by a<module_name>, then it enables the module to be executed as an executable file.You can refer to python docs for the same, or run
python --help这实际上是一个有趣的问题，所以让我们探索@jedwards链接的Pep 338， 。
-m标志最初提供了更简单的目的 - 将模块名称转换为脚本名称。在Python 2.4中，行为是：
这似乎不是很有用，但这就是当时所做的。 PEP 338进一步扩展了这一行为。
它继续解释说，Python将识别模块来自的软件包，使用标准过程导入该软件包，然后运行模块。据我了解，调用“ Python3 -M package.module”与调用相同：
-m标志将将模块运行为
__文件__，而不是__ MAIN __。它还将将本地目录插入SYS.Path，而不是脚本的目录。因此，它破坏了相对进口，尽管这不是故意的，因此作者建议始终使用绝对进口。这也取决于您将其称为“ Python3 -m package.module”的方式不同于“ python3 -m模块”。从理论上讲，它很简单 - 它加载了python并导入模块，而不是将代码倾倒到
__ Main __。。这是一个不同的导入系统，其行为不同。其中一些更改不是故意的，只有在实施后才发现。 Python的进口是一团糟，可以混淆。This is actually an interesting question, so let's explore pep 338 linked by @jedwards in the top comment.
The -m flag originally served a simpler purpose- to convert a module name into a script name. In python 2.4, the behavior was:
This doesn't seem very useful, but that's what it did back then. Pep 338 extends this behavior further.
It goes on to explain further that python will identify the package the module is from, import that package using the standard process, and run the module. From what I understand calling "python3 -m package.module" is the same as calling:
The -m flag will run the module as
__file__and not__main__. It will also insert the local directory into sys.path instead of the script's directory. It therefore breaks relative imports, although this was not intentional, and the authors therefore recommend to always use absolute imports. It also depends on how you call it- "python3 -m package.module" is not the same as "python3 -m module".In theory it's simple- it loads up python and imports the module instead of dumping the code into
__main__. In practice that has many effects. It's a different import system that behaves differently. Some of those changes were not intentional and were only discovered after implementation. Python's imports are a mess and it's okay to be confused.当有人说这个问题太简单而无法打扰时，这很难回答。
据我所知，实际目的是这样，因此您可以在不在目录中时使用点符号来运行脚本。
你可以运行
python -m path.to.my.happy.place而不是在
路径/to/to/my/happy和运行python place.pyAmazing this is so hard to answer when some people say the question is too simple to bother with.
As far as I can tell, the practical purpose is so you can use dot notation to run your script when you aren't in the directory.
You can run
python -m path.to.my.happy.placeinstead of being in
path/to/my/happyand runningpython place.py如果已安装了多个版本的Python，并且要升级PIP
pip install -upgrade pip您如何知道哪个Python版本会受到影响？它取决于壳的路径变量。在这种情况下，您可能还会受到警告。为了避免这种混乱使用-m，它在变量。这是-m的另一个优点。If you have multiple versions of python installed and you want to upgrade pip
pip install --upgrade piphow do you know which python version will be affected? it depends on path variable for the shell. You might also get warning in this case. To avoid this confusion use-mthen it looks in variable sys.path. This is another advantage of-m.