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