# Python主控端程式筆記
###### tags: `Development`,`Study`
## 目錄
[ToC]
## Flask
1. <https://blog.techbridge.cc/2017/06/03/python-web-flask101-tutorial-introduction-and-environment-setup/>
2. <https://zwindr.blogspot.com/2018/03/python-flask.html>
3. https://hackmd.io/@shaoeChen/SyP4YEnef?type=view
4. https://medium.com/@twilightlau94/rest-apis-with-flask-%E7%B3%BB%E5%88%97%E6%95%99%E5%AD%B8%E6%96%87-1-5405216d3166
5. https://www.itread01.com/content/1546450059.html (upload file)
6. https://medium.com/datainpoint/flask-web-api-quickstart-3b13d96cccc2
* __Server__
* Library
```python
from flask import Flask, request, ...(any lib needed)
from config import DevConfig # 自訂的config.py, 內含已定義之config_object
```
* Construction
```python
app = Flask(__name__)
```
* Configuration
```python
app.config[attributes] = values
```
or
```python
app.config.from_object(DevConfig)
```
to load attributes from self defined object (class).
All configuration attributes: <https://flask.palletsprojects.com/en/0.12.x/config/>
* Adding route and func
```
@app.route(url, methods)
def func():
~
```
url: where to access func( ).
methods: how clients request to server. ('GET', 'POST' or both, default is 'GET')
* __Client__
<https://requests.kennethreitz.org/en/master/api/>
```python
import requests # making HTTP requests
r = requests.get(url)
r2 = requests.post(url, data=your_data, files=your_file)
# .get to ask for response
# .post to send value (and get response of needed)
# .~(url, data=, )
```
Note that data and files are passed in dict form.
* __Communication__
[Flask](http://flask.palletsprojects.com/en/1.1.x/#api-reference) is built up with [Jinja](https://jinja.palletsprojects.com/en/2.10.x/) template engine and the [Werkzeug](https://www.palletsprojects.com/p/werkzeug/) WSGI toolkit. Thus, the messages passing between server and client must obey the [WSGI](https://wsgi.readthedocs.io/en/latest/learn.html) specification.
+ Client
Client would send request to server and get the response if needed. We used [requests](https://requests.kennethreitz.org/en/master/api/) tookit to send requests obeying the HTTP protocal. There are two methods of requests: GET and POST.
```python
import requests
url = 'http://127.0.0.1:5000'
r1 = resquests.get(url)
data = {'data': 'user_info',
'user': 'c95cc',
'password': '123456'}
file = {'file': [1,2,3,4,5,6]}
r2 = requests(url, data=data, files=file)
print(r1.text)
print(r2.status)
print(r2.json)
...
```
+ Server
```python
app = Flask()
# assigning your server configuration
# ...
# end of assignment
@app.route(url='/', methods=METHODS) # url can be modified if needed
def _func(): # The action when this url is activated
msg = request.json
if msg['user'] == 'c95cc'and msg[passward] == '123456':
return 'Legal user' # in response.txt
else:
return {'error':'self defined message'} # in response.json
```
* METHODS can be 'GET', 'POST' or ['GET', 'POST']
## Encoding and Decoding Image
The request/response messages is transmitted as stream, thes the encoding/decoding procedure before request/after response is needed.
Flask/requests api can transmit json format directly, whie the elements in the json should be encoded and decoded before the transition.
+ Encoding
uint8 image -> byte image -> byte string -> b64 format -> utf-8 format
```python
def b64_encode(img):
byte_str = cv2.imencode('.png', img)[1].tostring()
b64_str = base64.b64encode(byte_img).decode('utf-8')
return b64_str
```
+ Decoding
utf-8 format -> byte string -> np array -> uint8 image
```python
def b64_decode(b64_str):
byte_str = base64.b64decode(b64_str)
np_img = np.fromstring(byte_str, np.uint8)
img = cv2.imdecode(np_img, cv2.IMREAD_COLOR)
return img
```
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