Python學習筆記（四）：if語句

第四章 if語句

4.1 條件測試

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4.1.1 檢查是否相等

car = 'bmw'
print(car == 'bmw')
print(car == 'byd')
print(car != 'byd')

輸出結果：

True
False
True

• == 等於
• != 不等於
• >, >=, <, <= 大小於等於

4.1.2 檢查多個條件

car = 'bmw'
phone = 'iphone'
print(car == 'bmw' and phone == 'iphone')
print(car == 'byd' or phone == 'samsung')

True
False

• and 邏輯且
• or 邏輯或

4.1.3 檢查特定值是否在列表中

nums = [10, 20, 30]
print(30 in nums)
print(40 not in nums)

True
True

• in 在列表中
• not in不在列表中

4.1.4 布爾表達式

flag = True
flag = False

不多贅述

4.2 if語句

age = 15
if age >= 18:
	print("You are old enough")
	print("You can vote now")

沒有輸出結果

Python的if語句不需要加括號。注意冒號

4.2.1 if-else語句

age = 15
if age >= 18:
	print("You are old enough")
	print("You can vote now")
else:
	print("You are too young")
	print("Please wait for " + str(18-age) + " year(s)")

輸出結果:

You are too young
Please wait for 3 year(s)

4.2.2 if-elif-else語句

age = 15
if age >= 18:
	print("You are an adult")
elif age >= 12:
	print("You are a teenager")
else: 
	print("You are a child")

輸出結果：

You are a teenager

4.2.3 檢查列表是否爲空

nums = []
if nums:
	print("list is not empty")
else:
	print("list is empty")

輸出爲：

list is empty

4.2.4 if語句與布爾表達式

flag = True
if flag:
    print("YES")
else:
    print("NO")

輸出：

YES

不多贅述