[Python] Note-01

1. 若sequences (strings, lists, tuples) 為空, 則當 False. 和true / false 比較用 is / is not

2. Comparisons to singletons like None should always be done with is or is not,
    never the equality operators (Example from stackoverflow)

3. 愛用 in 跟 string.find()

4. Tuple 除了 packing / Unpacking, 在做 swap 時不用暫時變數, 且可以 return multi-values

    4.1 C program to swap two numbers

5. Python 沒有 ternary operator ?:
   
    5.1 推薦的 conditional expressions 寫法

6. 善用 enumerate (Example from seanlin's blog)

7. loop with else (Example from python tutorial)

Loop statements may have an else clause; it is executed when the loop terminates through exhaustion of the list (with for) or when the condition becomes false (with while), but not when the loop is terminated by a break statement.

8. Chained comparisons (if a < b < c <= d)

9. Default argument values (It's warning to use mutable as default values)

The default values are evaluated at the point of function definition ins the defining scope :

i = 5

def f(arg=i):
    print arg

i = 6
f()

Will print 5.

def f(a, L=[]):
    L.append(a)
    return L

print f(1)
print f(2)
print f(3)

 Will print :

[1]
[1, 2]
[1, 2, 3]

If you don't want the default to be shard between subsequent calls :

def f(a, L=None):
    if L is None:
        L = []
    L.append(a)
    return L

10. 用 join 來串接 list ()

11. 用 property 取代 getters, setters (From seanlin's blog)

class Egg(object):

    def __init__(self, price):
        self._price = price

    @property
    def price(self):
        return self._price * RATE
    
    @price.setter
    def price(self, value):
        self._price = value

12. Context managers (From seanlin's blog)