学习笔记-Python中if语句

示例

name_array = ['charles', 'mark', 'bill', 'vincent', 'william', 'joseph', 'james', 'henry', 'gary', 'martin']
for name in name_array:
	if name == 'mark':
		print(name.upper())
	else:
		print(name.title())

1. 条件测试

1.1 检查是否相等

>>> name = 'Mark'			#赋值
>>> name == 'Mark'			#判断：相等，返回True;
>>> name == 'Bill'			#判断：不相等，返回False;

1.2 字符不区分大小写检查是否相等

>>> name = 'Mark'			#赋值
>>> name == 'mark'			#判断：不相等，返回False；
>>> name.lower() == 'mark'	#判断：相等，返回True；

1.3 检查是否不相等

first_name = 'Mark'
if first_name != 'Bill':
	print("first name is not mark")

1.4 比较数字

age = 22
age == 22	#判断：相等，返回True；
if age != 18:
	print("age is" , age)

>>> age = 22
>>> age < 25		#返回True
>>> age <= 25		#返回True
>>> age > 20		#返回True
>>> age >= 20		#返回True

1.5 检查多个条件

1.5.1 使用and检查多个条件

等同于“与”运算。

>>> age1 = 18
>>> age2 = 22
>>> age1 >= 16 and age2 <= 25	#返回True
>>> age1 >= 20 and age2 <= 25	#返回False
>>> age1 >= 20 and age2 <= 20  	#返回False

1.5.2 使用or检查多个条件

等同于“或”运算。

>>> age1 = 18
>>> age2 = 22
>>> age1 >= 16 or age2 <= 25	#返回True
>>> age1 >= 20 or age2 <= 25	#返回True
>>> age1 >= 20 or age2 <= 20  	#返回False

1.6 检查特定值是否包含在列表中

>>> name_array = ['charles', 'mark', 'bill', 'vincent', 'william', 'joseph', 'james', 'henry', 'gary', 'martin']
>>> 'mark' in name_array		#返回True
>>> 'jack' in name_array		#返回False

1.7 检查特定值是否不包含在列表中

>>> name_array = ['charles', 'mark', 'bill', 'vincent', 'william', 'joseph', 'james', 'henry', 'gary', 'martin']
>>> 'mark' not in name_array		#返回False
>>> 'jack' not in name_array		#返回True

1.8 布尔表达式

Time_Flag = True
Time_Disable = False

2 if 语句

2.1 单 if 语句

age = 22
if age >= 20:
	print("age is", age)

2.2 if-else 语句

age = 22
if age >= 18:
	print("You are an adult")
else:
	print("You are still a minor")

2.3 if-elif-else 语句

age = 22
if age < 18:
	print("You are a minor")
elif age < 65:
	print("You are an adult")
else:
	print("You are an old man")

2.4 多个 elif 代码块

age = 22
if age < 4:
	print("You are a baby")
elif age < 18:
	print("You are a minor")
elif age < 65:
	print("You are an adult")
else:
	print("You are an old man")

2.5 省略 else 代码块

age = 22
if age < 4:
	print("You are a baby")
elif age < 18:
	print("You are a minor")
elif age < 65:
	print("You are an adult")
elif age >= 65:
	print("You are an old man")
print("All age groups are included")

2.6 多个 if 语句测试

age = 22
if age < 4:
	print("You are a baby")
if age < 18:
	print("You are a minor")
elif age < 65:
	print("You are an adult")
elif age >= 65:
	print("You are an old man")
print("All age groups are included")

3 使用 if 语句处理列表

3.1 检查特殊元素

name_array = ['charles', 'mark', 'bill', 'vincent', 'william', 'joseph', 'james', 'henry', 'gary', 'martin']
for name in name_array:
        if name == 'mark':
                print("You are " + name.title())
        elif name == 'bill':
                print("You are " + name.title())
        else:
                print("You are " + name.title())

3.2 确定列表不为空

name_array = []
if name_array:			#判断列表是否为空
        for name in name_array:
                print("You are " + name.title())
else:
        print("No name in the list")

3.3 使用多个列表

Aries_name = ['charles', 'mark', 'bill', 'vincent', 'william', 'joseph', 'james', 'henry', 'gary', 'martin']
Gemini_name = ['bob', 'john', 'thomas', 'dean', 'paul', 'jack', 'brooke']
for name in Aries_name:
	if name not in Gemini_name:
		print("You are " + name.title())
	else:
		print(name.title() + "is the same")