Python : 透過字串與數字轉換來做"進制轉換"

所有的非10進制數字都要以字串的型式表達，而數字一律是10進制表示。

因此進制轉換就只是字串轉數字或數字轉字串的差別。以下就針對這兩種狀況來說明。

● 字串轉數字

>>> int ('0x10', 16)  #必須告訴直譯器字串是哪種進制
16

Python : Tkinter (Button, Label, Entry, Listbox)

Tkinter 並不是一個很強大的GUI library, 但優點是, 他是Python官方支援的module, 且大部分的OS都有預先安裝它<Note 1>。 之後陸續出現的第三方GUI library相信都是由他啟發的。因此如果不是開發太複雜的GUI tool, 又想了解這個歷史悠久的library, 那就值得來了解他。

話不多說，直接上code:

step 1. 先來創一個空的視窗

from Tkinter import *
    
win = Tk()
win.title("Tk Gui")
win.resizable(width=False, height=False)
win.geometry("500x250")

win.mainloop()

Python : 調用模組的語法比較

以調用random模組中randint函數，印出隨機數字0~10來作範例

1. 函數呼叫透過: 模組.函數() 

    import random
    print random.randint(0,10)

2. 直接呼叫函數(), 但必須告訴直譯器調用模組中的哪個函數

    from random import randint

    print randint(0,10)  

3. 直接呼叫函數(), 直接告訴直譯器要引用模組中所有的函數。 會有函數名稱衝突的風險!

    from random import *
    print randint(0,10)

4. 在script中定義模組的新名稱, 呼叫方式: 模組新名稱.函數()
    import random as newname
    print newname.randint(0, 10)

Python : tuple, list, set, dict 整理與比較

python常用的四種container types: tuple, list, set dictionary

tuple: ()

    - save in order

    - read only

list: []

    - save in order

set: {}

dictionary: {key:value}

NOTE:

t = tuple([1,2,3])

>>>t[0]

1

Python : Use dictionary to simulate multi-dimension array

Since there is no array in Python. Use dictionary instead.

Follows are the example to initialize a 2x2 array

>>>a={}
>>>for i in range(4):
. . .      a[i/2, i%2] = i
>>> a
{ (0,1):1, (1,0):2, (0,0):0, (1,1):3 }
>>>a[0,1]
1

Python : string related

### Demonstrate join

>>> list = ['Nice', 'to', 'meet', 'you']
>>> ''.join(list)
Nicetomeetyou

>>> ' '.join(list)
Nice to meet you

>>>'_'.join(list)
Nice_to_meet_you

Python : Exception Handling

以parsing文字檔的內容來做例外處理的範例, parsing過程中其它列的內容可能和原本預設格式不同, 此時就會有例外產生:

with open('a.txt', 'r') as f:
    badLine = 0
    goodLine = 0
    totalLine = 0

    for line in f:
        try:
            d1, d2, d3 = line.split()
        except:
            badLine += 1    
        else:
            goodLine += 1
        finally:  
            totalLine += 1   

    print('totalLine : {}, badLine: {}, goodLine: {}'.format(str(totalLine), str(badLine), str(goodLine)))

Python : class method / static method / method

This is a good example for showing the difference between class method, static method and method in Python.

class Demo:     
    y=1 # class (or static) variable
    def __init__(self,z):
        self.z = z

    @classmethod
    def class_method(cls, x):
        return x + cls.y

    @staticmethod
    def static_method(x):
        return x  #cannot invoke cls.z

    def method(self, x):
        return x + self.z


print Demo.class_method(2)  # show 3
print Demo.static_method(2)  # show 2

#print Demo.method(2) #Error, must declare first
demo = Demo(2)
print demo.method(2) # show 4

Python : dictionary

Follows are the Dictionary example. Key and value can be string or number.

● Initial a dictionary
>>> d={'a':'Martin', 'b':'John'}

● Add new item
>>> d['c']='Mary'

● Add items
>>> d.update({'d':'Megan', 'e':'May'})

● Check item in a dictionary (return True/False)
>>> 'd' in d
True
>>> 'f' in d
False

● Enumerate the items in a dictionary
>>> for id, name in d.items():
...         print id, name

● Delete an item
>>> del d['a']