Management ## third-party libraries
> Python relatively fast hardware in place is provided by a large number of third-party libraries you use.
Management of third-party libraries website https://pypi.org/ ####
#### How to install third-party libraries
#### pip
> Pip is the python package management tools to solve the immediate package dependencies. It can easily manage third-party libraries (package).
>
> Similar to PHP in Composer, or Nodejs in npm, or in Linux yum.
How to use the ### pip
`Pip install the package name (library name)`
Note: If you have multiple python environments circumstances, you may need to use pip3
Such as installing pymysql library
`pip install pymysql`
### install the specified version of the package
`Pip install the package name == 'version
### search already installed package
`` Pip show package name
### view all installed packages
`pip list`
Replacement of the mirror source ### pip
```
PIP replace domestic installation source
Some pip domestic mirror
Ali cloud http://mirrors.aliyun.com/pypi/simple/
China University of Science and Technology https://pypi.mirrors.ustc.edu.cn/simple/
Watercress (douban) http://pypi.douban.com/simple/
Tsinghua University https://pypi.tuna.tsinghua.edu.cn/simple/
University of Science and Technology of China http://pypi.mirrors.ustc.edu.cn/simple/
Modify the source method:
temporary use:
It can be followed by the -i parameter specifies pip pip in the use of the source
pip install scrapy -i https://pypi.tuna.tsinghua.edu.cn/simple
Permanent modifications:
linux:
Modify ~ / .pip / pip.conf (not create one), reads as follows:
[global]
timeout = 6000
index-url = https://pypi.tuna.tsinghua.edu.cn/simple
trusted-host = pypi.tuna.tsinghua.edu.cn
windows:
Create a directory pip directly in the user directory, such as: C: \ Users \ xx \ pip, pip directory in the new document pip.ini, reads as follows
Or in accordance with the recommendations of friends: win + R to open the user directory% HOMEPATH%, pip create a folder in this directory, create a file in pip.ini pip directory, as follows
[global]
timeout = 6000
index-url = https://pypi.tuna.tsinghua.edu.cn/simple
trusted-host = pypi.tuna.tsinghua.edu.cn
```
## Virtual Environment
> Virtual environment is in the current system environment, in addition to the configuration of a python runtime environment, it can create a number of different virtual environments.
>
> Python virtual environment independent of each other.
+ Virtual environment can be installed in the new library without permission (problems may arise Linux system)
+ Different applications can use different or different repositories.
+ Library upgrade virtual environment does not affect other environmental
+ Virtual environment can be used as proprietary environment of a project. When you need to deploy, a key export items needed package
### How to use python virtual environment
1. You can create a virtual environment directly in the pycharm
#### 2. Install their own independent virtual environment
1. #### to create a virtual environment
`Python -m venv name` virtual environment
2. #### into the virtual environment, activate the virtual environment
+ linux
```shell
# Use the source command to execute activate under v1 / bin / directory
localhost:code yc$ source v1/bin/activate
(v1) localhost:code yc$
```
+ windows
```shell
# Windows system required to enter v1 / Scripts / directory
cd v1/Scripts/
# Run activate.bat file
activate.bat
(v1) F:\code>
```
3. #### then you can install some packages in a virtual environment
`pip install pymysql`
4. #### to see whether a package is installed
`Pip show pymysql` if installed is able to display information.
5. Exit virtual environment ####
+ linux : deactivate
+ Windows: direct ctrl + c
6. #### export package in the current environment of all installed
```shell
# View all installed packages
pip list
'''
Package Version
------------ -------
Click 7.0
Flask 1.1.1
itsdangerous 1.1.0
Jinja2 2.10.3
MarkupSafe 1.1.1
pip 19.0.3
PyMySQL 0.9.3
setuptools 40.8.0
tool 0.16.0
'''
# Export all packets to files
pip freeze > ./requirements.txt
```
7. Delete #### environment
After exiting the virtual environment, just delete the folder to a virtual environment
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