Python

Lambda

https://medium.com/better-programming/how-to-use-lambda-expressions-in-python-a96330b513d4

Lambda Example - 模擬 switch

在Python中缺少其它語言中的switch陳述句，以下結合字典物件與lambda模擬switch的示範

score = int(input('請輸入分數：'))
level = score // 10
{
    10 : lambda: print('Perfect'),
    9  : lambda: print('A'),
    8  : lambda: print('B'),
    7  : lambda: print('C'),
    6  : lambda: print('D')
}.get(level, lambda: print('E'))()

在上例中，字典物件中的值的部份是lambda所建立的函式物件，你使用get()方法指定鍵，如果有符合的鍵，就傳回對應的函式物件並執行，否則就傳回get()第二個引數所指定的函式並執行，這模擬了switch中default的陳述。

List (Slicing)

https://railsware.com/blog/python-for-machine-learning-indexing-and-slicing-for-lists-tuples-strings-and-other-sequential-types/

Import

Python的import陷阱

https://pyliaorachel.github.io/blog/tech/python/2017/09/15/pythons-import-trap.html

Flask

Get parameter

from flask import Flask, request
app = Flask(__name__)

@app.route('/')
def hello_world():
	paramStr = request.args.get('paramStr',type = str) 
	return paramStr

Input:

http://127.0.0.1:5000/?paramStr=test123中文

Output:

test123中文

Allow Cross-origin AJAX

Handling Cross Origin Resource Sharing (CORS), making cross-origin AJAX

pip install -U flask-cors

Simple Usage

from flask import Flask
from flask_cors import CORS

app = Flask(__name__)
CORS(app)

@app.route("/")
def helloWorld():
  return "Hello, cross-origin-world!"

https://flask-cors.readthedocs.io/en/latest/

Flask-Session

Managing Session Data in Flask with Flask-Session & Redis

https://hackingandslacking.com/managing-flask-session-variables-f4c5ccef54c0

run with https

https://stackoverflow.com/questions/28579142/attributeerror-context-object-has-no-attribute-wrap-socket/28590266#28590266

if __name__ == "__main__":
    context = ('cert.crt', 'key.key')
    app.run(host='0.0.0.0', port=80, ssl_context=context, threaded=True, debug=True)

if __name__ == '__main__':
    app.run(host="0.0.0.0", port=8080, ssl_context=('/etc/letsencrypt/live/mdminhazulhaque.io/fullchain.pem', '/etc/letsencrypt/live/mdminhazulhaque.io/privkey.pem'))

validate https cert

https://bits.mdminhazulhaque.io/python/run-flask-app-with-let's-encrypt-ssl-certificate.html

openssl s_client -quiet -connect mdminhazulhaque.io:8080

openssl s_client -quiet -connect emsd-voicebot-webhook.abapi.info:80

I got errno=0 which means Flask is working fine with SSL. :D

PEP8 standards - Style Guide

PEP 8 -- Style Guide for Python CodePython.org

Logging

Good logging practice

Good logging practice in PythonFang-Pen's coding note

import logging
logging.basicConfig(level=logging.INFO)
logger = logging.getLogger(__name__)

logger.info('Start reading database')
# read database here
records = {'john': 55, 'tom': 66}
logger.debug('Records: %s', records)
logger.info('Updating records ...')
# update records here
logger.info('Finish updating records')

Output:

INFO:__main__:Start reading database
INFO:__main__:Updating records ...
INFO:__main__:Finish updating records

change the logger level to DEBUG and see the output again

logging.basicConfig(level=logging.DEBUG)

Output:

INFO:__main__:Start reading database
DEBUG:__main__:Records: {'john': 55, 'tom': 66}
INFO:__main__:Updating records ...
INFO:__main__:Finish updating records

logging 教學

[Python] logging 教學Max的程式語言筆記

Numpy

Tips

机器学习中常用的Numpy函数_赵大寳Note的博客-CSDN博客_np.intersect

Pandas

Tips

實用但常忘記的Pandas Dataframe常用指令 1Medium

Tips

Determine if variable is defined

'a' in vars() or 'a' in globals()

if you want to be pedantic, you can check the builtins too 'a' in vars(__builtins__)

Determine if variable is defined in PythonStack Overflow

Code Example

list of dictionaries search

import logging
logging.basicConfig(level=logging.INFO)
logger = logging.getLogger(__name__)

people = [
    {'name': "Tom", 'age': 10},
    {'name': "Mark", 'age': 5},
    {'name': "Pam", 'age': 7}
]

def searchListDict(dataList, key='name', value=None):
    '''
    Searching a list of Dictionaries
    2018-05-16

    Param:  List of Dictionaries
    Return: Dictionary
    '''
    try:
        for l in dataList:
            if l[key] == value:
                return l

        logger.info('No Matching')
        return None # return None if finised looping & no matching

    except:
        logger.error('ERROR:', exc_info=True)

person = searchListDict(people, key='name', value='Pamx')
print(person)

min(None, x)

min(filter(lambda x: x is not None, lst)) if any(lst) else None

In [3]: lst = [None, 1, None]

In [4]: min(filter(lambda x: x is not None, lst)) if any(lst) else None
Out[4]: 1

In [5]: lst = [-4, None, 11]

In [6]: min(filter(lambda x: x is not None, lst)) if any(lst) else None
Out[6]: -4

In [7]: lst = [0, 7, -79]

In [8]: min(filter(lambda x: x is not None, lst)) if any(lst) else None
Out[8]: -79

In [9]: lst = [None, None, None]

In [10]: min(filter(lambda x: x is not None, lst)) if any(lst) else None

In [11]: print(min(filter(lambda x: x is not None, lst)) if any(lst) else None)
None

https://stackoverflow.com/questions/6254871/python-minnone-x

import numpy as np

lst = [1, 2, 3, 4, 5, None]

x = np.array(lst, dtype=np.float64)
print(x)
# array([  1.,   2.,   3.,   4.,   5.,  nan])

https://stackoverflow.com/questions/46025724/getting-max-value-from-a-list-with-none-elements

Get Max Value in Dict

def keywithmaxval(d):
     """ a) create a list of the dict's keys and values; 
         b) return the key with the max value"""  
     v=list(d.values())
     k=list(d.keys())
     return k[v.index(max(v))]

https://stackoverflow.com/questions/268272/getting-key-with-maximum-value-in-dictionary

Tools

Automated RESTful API testing

Tavern

https://taverntesting.github.io/examples

Protect code

Protecting a Python codebaseTheoremOne Blog

Protecting Python Sources With CythonMedium

GitHub - Falldog/pyconcrete: Protect your python script, encrypt it as .pye and decrypt when import itGitHub

Troubleshoot

Mac OS X: ValueError: unknown locale: UTF-8

add these lines to your ~/.bash_profile

~/.bash_profile

export LC_ALL=en_US.UTF-8
export LANG=en_US.UTF-8

Mac OS X: ValueError: unknown locale: UTF-8 in Python (Example)Coderwall

ERROR: FutureWarning: Conversion of the second argument of issubdtype from `float` to `np.floating` is

FutureWarning: Conversion of the second argument of issubdtype from float to np.floating is deprecated. In future, it will be treated as np.float64 == np.dtype(float).type. from ._conv import register_converters as _register_converters

Problem: h5py issue (2.7.1

Solution: upgrade h5py (2.9.0)

pip install --upgrade h5py

17個新手常見的Python運行時錯誤

https://www.oschina.net/question/89964_62779

ERROR: ImportError: cannot import name 'Flask'

Problem: error while import 'flask'

>>> from flask import Flask
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/ryan/Python/github/flask/flask.py", line 9, in <module>
    from flask import Flask, jsonify, request, session
ImportError: cannot import name 'Flask'

Solution: The reason is your python file name is 'flask' in same directory.