變量、常量、input、if語句

Chapter2 Python基礎

2.1 變量命名規則

• 字母、數字、下划線組成
• 不能數字開頭
• 不能使用python中的關鍵字
• 變量名具有意義
• 推薦駝峰（ArvinGood）、或者下划線方式 (arvin_good) 命名

標准示例：

your_name = 'Jack Ma'

2.2 常量

• 全部大寫的變量名就是常量 ARVIN = 99

示例：

ARVIN_AGE = 18

2.3 注釋

• 三種方式：
  1. “#”號單行注釋
  2. ‘’‘三個單引號和三個雙引號”“”進行多行注釋

例：

# The idle boy is almost invariably poor and anxious. 單行注釋

'''
這是多行注釋示范
'''

"""
多行注釋示范
"""

2.4 輸入輸出

• 用戶輸入 input
  1. 注意：input獲取到的內容都是字符串類型
• 用戶輸出 print
  1. print打印出內容

your_id = input("input your id identifier: ")
your_pwd = input("input your password: ")
print("Your id is {}, Your password is {}".format(your_id, your_pwd))

運行結果：
input your id identifier: Jack
input your password: default
Your id is Jack, Your password is default

2.5 五種if條件判斷語句

• 單if條件判斷

  if 條件： #條件判斷 > < ==

  ​ print(‘真實’) #條件成立則執行

  if 10 > 8:
      print("You are right.")
  

• if else條件判斷

  if 10 > 20:
  	print("10 is bigger than 2.")
  else:
  	print("10 is smaller than 2.")
  

• if elif elif else 條件判斷

  a = "jack"
  if 10 > 50:
  	print("10 is bigger than 5.")
  elif type(a) == "str":
  	print("a is a string.")
  elif 20 == 20:
  	print("20 is equal 20.")
  else:
      print("All of them are false.")
     
  運行結果：
  20 is equal 20.
  

• 多個同級if語句

  a = "jack"
  if 10 == 20:
  	print("10 is equal 20.")
  if a == "jack":
  	print(a ,"is the same as jack.")
  if 10 == 10:
  	print("10 is equal 10.")
      
  運行結果：
  jack is the same as jack.
  10 is equal 10.
  

• if與if語句之間的嵌套

  id = int(input("input your id number: "))
  pwd = input("input your passwrd: ")
  if id == 9:
  	print("GO ON.")
  	if pwd == "default":
  		print("You logged in successfully.")
  	else:
  		print("Your password is incorrect.")
  else:
  	print("Your id was typed incorrectly.")