python intro 2

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 …