Python Learning: 02

　　OK, let's continue.

• Conditional Judgments and Loop
  • if
  • if-else
  • if-elif-else
  • while
  • for
  • break
  • continue
  • multiple loop

• Differences between Dict and Set
  • Dict: A kind of structure in the type of "Key-Value"
    • described in "{}"
    • formed by "key: value"
    • function "len()" to calculate the length
    • judge empty：① if 'key' in dict  ②dict.get('key')  ->if empty, return None automatically
    • the key in dict is unchangeable
  • Set: A kind of struture in the type of Non-repeating elements collection
    • described in "set([,,,,])" 
    • add() to add elements
    • remove() to delete elements
• Functions
• where to searching functions:

  http://docs.python.org/2/library/functions.html#abs

• some common functions: abs(), cmp(), int(), str(), sum() 
• the Return Value of Functions

　　　　　　　　A function can return single value, as well as return more value. But in essence it returns one, a tuple. The function treats the values as a tuple.

>>> r = move(100, 100, 60, math.pi / 6)
>>> print r
(151.96152422706632, 70.0)

• • recursive functions: 　take care of overflowing
  • default parameter: set default parameter in the function line in the blankets, and the default parameter must be set at the right side 
  • variable parameter: use '*' to mark variable parameter , and they are regarded as a tuple