if语句

比较：

==、!=、<、<=、>、>=

in、not in

and、or

if语句:

if

age = 19
if age >= 18:
    print("you re old enough to vote!")
输出
you re old enough to vote!

if-else

age = 17
if age >= 18:
    print("you re old enough to vote!")
else:
    print('sorry,you re too young to vote')
输出
sorry,you re too young to vote

if-elif-else

age = 12
if age < 4:
    price = 0
elif age < 18:
    price = 5
else:
    price = 10
print("Your admission cost is $" + str(price) + '.')
输出
Your admission cost is $5.

names = []
if names:
    print("True")
else:
    print("False")
输出
False  #Python将在列表至少包含一个元素时返回True，并在列表为空时返回False

简写

print('alex is a good man') if name == 'alex' else print("wrong")
(表达式1)                    if (条件)          else (表达式2)   #如果条件成立，执行表达式1，否则执行表达式2