Python——Win10用Python3写Flask

按照Flask官网安装教程来安装Flask。

1. 安装venv，venv是一个python的虚拟环境，可以隔离工程环境和全局环境。

cd yourProjectPath
py3 -m venv yourVenvFolderName

2. 启动venv

yourVenvFolderName\Scripts\activate

如果你的Scripts\下没有activate文件，参照StackOverflow: venv doesn't create activate scrpt python3，你需要换一种不带pip的方式创建venv

py3 -m venv --without-pip yourVenvFolderName

3. 安装Flask
   用pip安装Flask，你的虚拟环境里可能由于某种原因没有pip，例如采用上面--without-pip的方式安装，会报错。

(venv) F:\xxx>pip install Flasksk
Fatal error in launcher: Unable to create process using '"xxx:\python\python3.8.2\python.exe"
"xxx\Python3.8.2\Scripts\pip.exe" install Flask': ???????????

那么需要先在虚拟环境里再安装一个pip。
注意：如果你安装了多个版本的python，并且为了方便把python.exe重命名了，例如本文之前的命令都是用我自己重命名的py3代替python，那么这里执行安装pip的命令前你需要暂时重命名回原本的“python.exe”。

否则会报错，在安装pip时依赖的wheel找不到：
（ps：这里应该有更好的办法可以直接用重命名后的py3，但是暂时先这样解决）

-- 错误命令：
curl https://bootstrap.pypa.io/get-pip.py | py3

% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 1764k 100 1764k 0 0 17378 0 0:01:44 0:01:44 --:--:-- 40227
Collecting pip
Using cached pip-20.0.2-py2.py3-none-any.whl (1.4 MB)
ERROR: Could not find a version that satisfies the requirement wheel (from versions:
none)
ERROR: No matching distribution found for wheel

-- 正确命令：
curl https://bootstrap.pypa.io/get-pip.py | python

% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 1764k 100 1764k 0 0 5034 0 0:05:59 0:05:59 --:--:-- 13847
Collecting pip
Using cached pip-20.0.2-py2.py3-none-any.whl (1.4 MB)
Collecting wheel
Downloading wheel-0.34.2-py2.py3-none-any.whl (26 kB)
Installing collected packages: pip, wheel
Attempting uninstall: pip
Found existing installation: pip 20.0.2
Uninstalling pip-20.0.2:
Successfully uninstalled pip-20.0.2
Successfully installed pip-20.0.2 wheel-0.34.2

验证pip是否安装成功

(venv) F:\xxx>pip --version
pip 20.0.2 from d:\python\python3.8.2\lib\site-packages\pip (python 3.8)

成功安装pip，然后安装Flask

pip install Flask

安装Flask的过程中会自动安装几个依赖Werkzeug、Jinja2、itsdangerous、click、MarkupSafe。
安装依赖的过程中可能由于网络原因而失败，例如：

Collecting Werkzeug>=0.15
WARNING: Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after
connection broken by 'ReadTimeoutError("HTTPSConnectionPool(host='files.pythonhosted.org', port=443): Read timed out. (read timeout=15)")':
...
Downloading Werkzeug-1.0.1-py2.py3-none-any.whl (298 kB)
ERROR: Exception:
Traceback (most recent call last):
...
socket.timeout: The read operation timed out

这时可以换个国内的镜像。
或者直接科学上网，几秒钟就可以安装完毕了。

Collecting Flask
Using cached Flask-1.1.2-py2.py3-none-any.whl (94 kB)
Collecting Werkzeug>=0.15
Downloading Werkzeug-1.0.1-py2.py3-none-any.whl (298 kB)
|████████████████████████████████| 298 kB 198 kB/s
Collecting Jinja2>=2.10.1
Downloading Jinja2-2.11.2-py2.py3-none-any.whl (125 kB)
|████████████████████████████████| 125 kB 652 kB/s
Collecting itsdangerous>=0.24
Using cached itsdangerous-1.1.0-py2.py3-none-any.whl (16 kB)
Collecting click>=5.1
Downloading click-7.1.1-py2.py3-none-any.whl (82 kB)
|████████████████████████████████| 82 kB 260 kB/s
Collecting MarkupSafe>=0.23
Downloading MarkupSafe-1.1.1-cp38-cp38-win32.whl (16 kB)
Installing collected packages: Werkzeug, MarkupSafe, Jinja2, itsdangerous, click, Flask
Successfully installed Flask-1.1.2 Jinja2-2.11.2 MarkupSafe-1.1.1 Werkzeug-1.0.1 click-7.1.1 itsdangerous-1.1.0