阿葛廷

人一定要靠自己!

4 minute read

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Python function

  • funcion 
     def function_name(parameters):
    # code...

 def greet():
    print("Hello!")
  • return statement 
     def square(x, y):
     return x*x, y*y

 res_x, res_y =square(2, 3)
 print(res_x) # 4
 print(res_y) # 9
  • anonymous function - lambda 
     double = lambda x: x *2

 print(double(5)) # 10

 # Lambda functions can have any number of arguments
 double = lambda x, y: x*2 + y

 print(double(5,2) # 12

Python Generators

  • Generator with for loop 
     def generator_example():
    a = 1
    yield print(a) # 1
    a += 1 
    yield print(a) # 2
    return
    
  for i in generator_exmple():
      continue

  # Output:
  # 1 
  # 2
  • Generator with next, avoid StopIteration Error 
     def generator_example():
    yield print(1)
    yield print(2)
    return

 gen = generator_example()
 gen.__next__() # 1
 gen.__next__() # 2
 gen.__next__() # Traceback (most recent call last): 
                #  File "<stdin>", line 1, in <module>
                # StopIteration

 # avoid StopIteration Error
 try: 
      gen.__next__()
  except StopIteration:
      pass
  • Benefits - Memory Usage 
     # 利用 list 迭代
 range_num = 10
 for i in [x*x for x in range(range_num)]:
     # do something
     pass

 # 利用 generator 迭代
 for i in (x*x for x in range(range_num)):
     # do something
     pass
    • Memory Usage - by using list 
       import psutil
 before_used = psutil.virtual_memory().used  # expressed in bytes
 after_used = 0
 print("before:", before_used)
      
 range_num = 1000000
 for i in [x*x for x in range(range_num)]: # 第一種方法：對 list 進行迭代
     if i == (range_num - 1) * (range_num - 1):
         after_used = psutil.virtual_memory().used
         print("after:", after_used) 
      
 print("used memory:", (after_used - before_used))    
      
 """
 before: 6833217536
 after: 6859653120
 used memory: 26435584
 """
    • Memory Usage - by using generator 
       import psutil
 before_used = psutil.virtual_memory().used  # expressed in bytes
 after_used = 0
 print("before:", before_used)
      
 range_num = 1000000
 for i in (x*x for x in range(range_num)): # 第二種方法：對 generator 進行迭代
     if i == (range_num - 1) * (range_num - 1):
         after_used = psutil.virtual_memory().used
         print("after:", after_used) 
      
 print("used memory:", (after_used - before_used))

 """
 before: 6848933888
 after: 6850170880
 used memory: 1236992
 """

Modules

  • Modules 
     import re

 import re as r

 from re import findall

 from re import *
  • Module - os 
     import os
 # 顯示絕對路徑
 os.path.abspath("")
   
 # 將多個字串組合為路徑
 "/".join(['path', 'result', 'a.csv'])
   
 # 將多個字串組合為路徑
 os.path.join('path', 'result', 'a.csv')
   
 # 檢查某路徑 /資料夾是否存在
 os.path.exists("path/session_1-ans.ipynb")

Regular Expression

  • re 
     "This is demo string, do nothing!"

 # pattern_1
 "is"

 # pattern_2
 "abc"

 # find - does the string contains the pattern?
 # YES or NO

     "This is demo string, 01234567899876543210"

 # pattern
 "01234567899876543210"

 # if you want to search more complex pattern?
 # using regular expression!

 syntax = "[0-9]{20}"

    • Special Characters

       .     match any character except a newline 
 *     match 0 or more repetitions of the preceding character
 +     match 1 or more repetitions of the preceding character
 {m}   match exactly m copies of the previous character
 {m,n} match from m to n repetitions of the preceding character
 \     escapes special characters
 [ ]   Used to indicate a set of characters 
    [amk] will match 'a', 'm', or 'k'
    [a-z] will match any lowercase ASCII letter
    [0-5][0-9] will match all the two-digits numbers from 00 to 59

  • Module - re

     import re
   
 string = "This is demo string, do nothing!"
 pattern = "is"
   
 # Return a list of all non-overlapping matches in the string.
 print(re.findall(pattern, string))  # ['is', 'is']

     import re

 # find numbers
 pattern = "[0-9]+"
 string = "12 drummers drumming, 111 pipers piping, 1006 lords a-leaping"
 re.findall(pattern, string)  # ['12', '111'. '1006']

 # find letters 
 pattern = "[cmf]an"
 string = "find: can, man, fan, skip: dan, ran, pan"
 re.findall(pattern, string) # ['can', 'man', 'fan']
    • find e-mail 
       import re
 email_text= """ Big Data Analytics/ Deep LearningSocial Computing / Computational Social Science / Crowdsourcing Multimediaand Network SystemsQuality of ExperienceInformation SecurityPh.D. candidate at NTU EEchihfan02-27883799#1602Camera CalibrationComputer VisionData Analysiscmchang02-27883799#1671System OptimizationMachine LearningyusraBig data analysiscclin02-27883799#1668Data Analysisrusi02-27883799#1668Government Procurement ActFinancial Managementkatekuen02-27883799#1602AdministrationEvent Planningseanyu02-27883799#1668Data AnalysisPsychology & NeuroscienceMarketingxinchinchenEmbedded Systemkyoyachuan062602-27883799 #1601FinTechActuarial ScienceData Analysiskai0604602-27883799#1601Data AnalysisMachine Learningchloe02-27839427Accountingafun02-27883799 felix2018@iis.sinica.edu.tw #1673Data AnalysisWeb developmentyunhsu198902-27883799#1668MarketingTIGP Ph.D. Fellow at Academia Sinica & NCCUbaowalyMachine LearningData AnalysisSocial Computingchangyc1427883799#1678 Data Analysisjimmy1592302-2788379 jimmy15923@iis.sinica.com.tw#1688Data AnalysisjasontangAnalysisMachine Learninguchen02-27883799#1668Deep Learningpjwu02-27883799#1604Computational PhotographyData Analysis """

 re.findall("([A-Za-z0-9._]+@[A-Za-z.]+[com|edu]\.tw)", email_text) # ['felix2018@iis.sinica.edu.tw', 'jimmy15923@iis.sinica.com.tw']

  • Class

     class MyClass:
    var = 123
    def method(self):
       return "hello world"

 # Instantiation
 my_object = MyClass()
    • init, self 
       # no arguments
 class MyClass:
     def __init__(self):
         print("do nothing")

 # with arguments
 class MyClass:
     def __init__(self, var1, var2):
         self.var1 = var1
         self.var2 = var2
    • Object 
       class MyClass:
     def __init__(self, var1):
         self.var1 = var1
      
 my_object_123 = MyClass(123)    # <__main__.MyClass object at 0x7f2008391438>
 my_object_987 = MyClass(987)    # <__main__.MyClass object at 0x7f20083916a0>
      • example 
         class Person:
    bmi = 0.0
    height = 0.0
    weight = 0

    def __init__(self):
        pass

    def ask_person_info(self):
        self.height = float(input("What is your height? (meter) : "))
        self.weight = int(input("What is your weight? (kg) : "))

    def cal_BMI(self):
        self.bmi = round((self.weight / (self.height ** 2)), 2)
        print("Your BMI is " + str(self.bmi))

jupyter notebook 快捷鍵

  • ESC 跳出 cell

  • Enter 進入 cell

  • run cell
    • Shift-Enter : 執行完跳下一行
    • Ctrl-Enter : 執行完留在同一行
    • Alt-Enter : 執行完insert下一行
  • Cell 新增、移除、合併
    • A : insert cell above
    • B : insert cell below
    • X : cut selected cells

    • C : copy selected cells

    • Shift + V : pasts cells above
    • V : pasts cells below
    • Z : undo cells deletion
    • D D : delete selected cells
    • Shift + M : merge selected cells, or current cell with cell below if only one cell is selected
  • 改變 cell 功能 (code、markdown、raw)
    • Y : change cell to code
    • M : change cell to markdown
    • R : change cell to raw
  • edit mode
    • TAB : code completion or indent / (提供輸入選項)
    • function 提示說明:
      • Shift + TAB : tooltip
      • Shift + TAB + TAB : tooltip + parameters
  • Jupyter notebook 魔術指令
    • %
      • %cd : 改變路徑
      • %save: 將 cell 儲存為 .py
      • %run xxx.py: 執行 xxx.py 檔
      • %timeit: 計算該 cell 執行之時間
      • %matplotlib inline: 將繪製的圖直接顯示在 notebook 上
      • %matplotlib notebook
    • ! 可以直接輸入 terminal 的指令
      • !nvidia-smi
      • !ls
      • !rm
      • !pip install …

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