一个简单示例

cars = ['bmw', 'audi', 'toyota', 'subaru']
for car in cars:
    if car == 'bmw':
        print(car.upper())
    else:
        print(car.title())

BMW
Audi
Toyota
Subaru

条件测试

# 检查是否相等 (区分大小写)
car = 'Audi'
print(car == 'audi')
# 不相等
print(car != 'audi')

False
True

# 比较数字
age = 19
print(age == 19)
print(age != 19)
print(age < 21)
print(age <= 21)
print(age > 21)
print(age >= 21)

True
False
True
True
False
False

# 检查多个条件
# and 同时成立; or 至少一个满足 
age = 19
print(age > 10 and age < 19)
print(age > 10 or age < 19)

False
True

# 是否包含
# in 包含; not in 不包含
users = ['a001', 'a002', 'a003']
print('a003' in users)
print('a004' not in users)

True
True

# 布尔表达式
status1 = True
status2 = False

cars = []
if cars:
    print("cars is not null")
else:
    print("cars is null")

cars is null

列表是空, 做为条件是False

if condition_1:
    statement_block_1

if condition_1:
    statement_block_1
else:
    statement_block_2

if condition_1:
    statement_block_1
elif condition_2:
    statement_block_2
else:
    statement_block_3

if condition_1:
    statement_block_1
elif condition_2:
    statement_block_2
elif condition_3:
    statement_block_3
else:
    statement_block_4

Python3 目录