3.1 python学习笔记本

what it is

-   we don't need to "declare" `spam_amount` before assigning to it
-   we don't need to tell Python what type of value `spam_amount` is going to refer to. In fact, we can even go on to reassign `spam_amount` to refer to a different sort of thing like a string or a boolean.

• The colon (:) at the end of the if line indicates that a new code block is starting

• Subsequent lines which are indented are part of that code block.

• Strings can be marked either by double or single quotation marks.

  • if strings are including a variable(single quote),"" is better.

your function

first to write a docstrings

• default argument can be added by (num_child = 3)

• no return function is none = NULL in other language.

• help() insert the function to help ,which is can be your own coded function.

• 函数有一个default参数，如果我们传入自己的参数覆盖那么会返回该参数，否则会使用系统默认的参数。因此我们需要先用Help文档查阅参数。

• use def before naming the function. and end with a:!!!!

• 函数嵌套，higher-order functions 中文文档我害怕有一天我读不懂英文，突然有一天，不过想一想，英文和中文也差不多一样的烂。

• conditional operator

    should to be `True` or `False`
    `and or not ` VS `&& || !` in c++
    
    - to  improve the readibility ,we should add more parentheses.
    
  

• if elif VS else : after each statement

• invert function transfer the content's type compulsorily , bool(x),except 0 is 1.which means only bool(0) = False,so too does the empty string or char

• sign function

  to justify the sign of a numerical input .

  print("Splitting", total_candies, "candy" if total_candies == 1 else "candies")
  

python can directly calculate the boolen as (0 or 1) as arithmetic

• list

     1. different from c++ , 'list string variable is a single or double (=) be a member of list.
     2. not the curly parentheses we use the square brackets[]
     3. mix of all the availble types,help is accessible !!!
     4. the index is from 0,also [-1] [-2]...
     5. slicing [:2] = [0],[1];      [2:] = [2], [3], [4], .......till the end of this list.!     [1:-1] = [1], [2], ....[end]
         [-3:] = [-3], [-2], [end]
     6. bin(int ) return its binary item
     
     
  

  • len(list)
  • sorted(list) in alphabetical
  • sum(list)
  • min/max(list)

• everything in python is an object

  • attribute: non function of the object

  • method : function of the object ! when we call the funciton ,we should add a parenthese () to the end of the function name

  • list. append(int ) add this int in the end of the list

  • list . pop()

  • list.index()

  • conditional operator in : int in list

• tuple

  • () not []
  • the elements in the tuple is not modified (inmutable)
  • can be used to represent the multiple value of a object!

a, b = b, a

• loops

  • tuple,list, string all the element in this iterable things

• range()

• for while dont have a ()

• many sentences can be concluded in a []

• any return iterable in list to classify any ele in the list

• string """ """ docstring can cotain a enter (= \n) python auto add a \n ,so we need to add a sep= ' '

• like a list function but can not to be modified

• str.split('-')whitespace a list

• '' .join['s','a','d']

• +,only str can be sewed to be a long atr

{}",format(a)

keys to be the index nums[key] to get its value

nums.values() nums.keys() nums.items() return key and value

help(str)