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Python Study (2) - Concept

 
  • Study travel beginning
       Execute your first code Hollow World
        >>> print("Hollow World")
         Hollow World


    Python's core Data Type
           We understand  data type before studying any program. Python has built-in object types


    Data Type(Object type) Example
    Numbers int, float, long, complex
    Strings  
    Lists  
    Dictionaries  
    Tuples  
    Files  
    Sets set, frozenset
    Primitive types boolean,
    Program unit types Functions, modules, classes
    Implementation-related types compiled code, stack tracebacks


    1. Number
        Example: real number, float, double ...
    >>> 333 + 555
        888
    >>> 333 / 111
       3.0
    >>> 333 * 9
       2997
    >>> "happy " * 2 + " birthday"
       'happy happy  birthday'

    Module : math and random
    >>> import math
    >>> math.pi
    3.141592653589793
    >>> import random
    >>> random.random()
    0.7082048489415967
    >>> random.choice([2,4,6,8])
    4
    Note : intelligent complement => tab

     

    2. String
    (1) String is a array of char

    >>> S = 'Money'
    >>> S[0]
    'M'
    >>> S[-1]
    'y'
    >>> S[0:-1]
    'Mone'
    >>> len(S)
    5
    >>> S[:]
    'Money'
    >>> S[1:]
    'oney'
    >>> S[:3]
    'Mon'

    (2) Unicode String
    https://docs.python.org/2/howto/unicode.html.
    Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed.Python’s strings also come with full Unicode support  required for processing text in internationalized character sets.
     
    Python 2.X  
         In python 2.X, All Strings represent a collection of bytes, Python is default ASCII
         script. If you want change non-ASCII script for the script, you need put first line
         to declare encoding declaration.
       
         * Use Python Script edit the code and run . Ref: Use IDLE
          
         The length of the string is not 2 but rather 4, because each chinese word
         contain 2 bytes. len() function return length of bytes
       

    # coding=big5
    text = "哈囉"   #The word is a Chinese word than meas "hello"
    print len(text)

    4  # the result after run


        What does it happen when use encoding declaration. The result return 2 length
        of the string.

    # coding=big5   #encoding declaration
    text = u"哈囉"      #python 2.x use “u” to represent Unicode
    print len(text)

    2  # the result after run

     
         Note:  Python 2.x need to declarate encoding declaration.
         Both 3.X and 2.X use  “\x” hexadecimal  and  “\u” to represent Unicode

    >>> text = u’哈囉’
    >>> text
    u'\xab\xa2\xc5o'

     


    Python 3.x        
        Python 3.x all strings are unicode encode.

    text = "哈囉"   #The word is a Chinese word than meas "hello"
    print(len(text))

    4  # the result after run
              

    Encode and decode

    function description example
    unichr(int ) return unicode

    >>> unichr(80)
    u'P'

    chr(int ) return integer

    >>> chr(80)
    'P'

    ord(str ) return ASCII or Unicode

    >>> ord(u'A')
    65

    encode(str) return encode string >>>
    decode(str) return decode string  
    unicode return unicode string  

    (3) Pattern Matching
    Module : re


    >>>import re
              

    3. Lists
    Lists are ordered arbitrary collection of objects and they have no fixed size.they are sequence objetcs

    >>> L = ["toast", 10, "toast with egg", 12.5, "toast with ham", 15]
    >>> len(L)
    6

    >>> L[0:2]
    ['toast', 10]

    >>>L[:-1]
    ['toast', 10, 'toast with egg', 12.5, 'toast with ham']

    >>>L + ["toast with vegetable", 20]
    ['toast', 10, 'toast with egg', 12.5, 'toast with ham', 15, 'toast with vegetable', 20]
              
    List functions
    function description example
    append add object at end of list >>> L.append(“toast with vegetable”)
    >>> L
    ['toast', 10, 'toast with egg', 12.5, 'toast with ham', 15, 'toast with vegetable']
    pop get object and remove >>> L.pop(-1)
    >>> L
    ['toast', 10, 'toast with egg', 12.5, 'toast with ham', 15]
    sort sort

    >>> M = ["Banana","Apple","Orange"]
    >>> M.sort()
    >>> M
    ['Apple', 'Banana', 'Orange']

    reverse  

    >>> M.reverse()
    >>> M
    ['Orange', 'Banana', 'Apple']

    keys return keys of the list  
    values return values of the list  

    List Arrary

    >>> L= [ [ 'toast','toast with egg','toast with ham','toast with vegetable'],
             [10,12.5,15,20]]
    >>> L[0]
    ['toast', 'toast with egg', 'toast with ham', 'toast with vegetable']

    >>> [row[1] for row in L]
    ['toast with egg', 12.5]
              
    range(int) : A built-in function is used to generate integers

    >>>List(range(5))
    [0,1,2,3,4]

    >>>for i in range(4):
                print(i)

    0
    1
    3
    4

    >>> list(range(1,4))
    [1,2,3]

    >>> list(range(1,8,2))
    [1, 3, 5, 7]
              
    map(function, iterable, ...) : map is a build-in function. Apply function to every item of iterable and return a list of the results.


    >>>List(range(5))

    >>> list1 = [1,2,3]
    >>> list2 = [1,2,3]
    >>> def sum(a,b):
        return a+b

    >>> list(map(sum, list1, list2))  #python 3.x use a list to store map 
    [2, 4, 6]
    >>>

              

    Dictionaries
    (1) kye/value
    (2) sequence


    >>> food = {"toast": 10, "toast with egg": 13.5, "toast with ham":15}
    >>> food["toast with egg"]
    13.5

    >>> food["toast with egg"]+=1
    >>> food["toast with egg"]
    14.5

    >>> food["toast with vegetable"] = 20
    >>> food["toast with vegetable"]
    20

              
    Dictionaries function

    dict : It is a name=value format and make dictionaries

    >>> newfood = dict(toast=15, toast_with_egg=20, toast_with_ham=25)}>>> newfood[toast_with_egg]
    Traceback (most recent call last):
      File "<pyshell#19>", line 1, in <module>
        newfood[toast_with_egg]
    NameError: name 'toast_with_egg' is not defined

    >>> newfood["toast_with_egg"]
    20

              

    zip :
    function :  zip([key1, key2, key3….], [value1, value2, value3…])

    >>>  dict(zip(['toast','toast with egg','toast with ham'],[10,12.5,15]))
    >>> newfood2["toast"]
    10

              
    build-in function

    >>> food= [ [ 'toast','toast with egg','toast with ham','toast with vegetable'],
             [10,12.5,15,20]]

            
    function description example
    keys show keys of the list

    >>> food.keys()
    ['toast', 'toast with ham', 'toast with vegetable', 'toast with egg']

    sort sort value of the list

    >>> foodMoney = list(food.values())
    >>> foodMoney.sort()
    >>> foodMoney
    [10, 14.5, 15, 20]

    values get values of the list

    >>> foodMoney = list(food.values())
    >>> foodMoney
    [10, 15, 20, 14.5]

    reverse  

    >>> foodMoney = list(food.values())
    >>> foodMoney.reverse()
    >>> foodMoney
    [20, 15, 14.5, 10]

       


    Tuples
    (1) sequence
    (2) fixed size
    (3) immutable (when the tuple is created, it connot be changed)

    >>> fruit = ("apple","organe","grape","banana")
    >>> fruit
    ('apple', 'organe', 'grape', 'banana')

    >>> fruit[0]
    'apple'

              
    built-in function

    >>> fruit = ("apple","organe","grape","banana")
    >>> fruit
    ('apple', 'organe', 'grape', 'banana')

    >>> fruit[0] = "tomato"
    Traceback (most recent call last):
      File "<pyshell#86>", line 1, in <module>
        fruit[0] = "tomato"
    TypeError: 'tuple' object does not support item assignment

              
    function description example
    index(object) return index of the tuple

    >>> fruit.index("banana")
    3

    count(object) return times of appear object in the tuple

    >>> fruit.count("apple")
    1









     

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