1. 条件语句
- 布尔表达式：True/False
- 一个等号是陈述，两个等号则是反问
1.1 == / is
- == 用于比较两个对象的值是否相等。
- is 用于检查两个对象是否指向同一个内存位置
x = 5
y = 5
print(f'x == y: {x == y}, x is y: {x is y}')
s1 = "hello"
s2 = "hello"
print(f's1 == s2: {s1 == s2}, s1 is s2: {s1 is s2}')
list1 = [1, 2, 3]
list2 = [1, 2, 3]
print(f'list1 == list2: {list1 == list2}, list1 is list2: {list1 is list2}')
# list1 == list2: True, list1 is list2: False
1.2 条件控制语句
语法：
if condition1:
...
elif condition2:
...
else:
...
示例：
age = 25
if age < 20:
print("age less than 20")
elif age > 20:
print("age more than 20")
else:
print("age = 20")
1.3 多条件：and / or
age = 25
if age > 20 and age < 30: # if 20 < age < 30:
print('age between(20, 30)')
if age > 20 or age < 10:
print(f'age is {age}')
1.4 包含: in
cats = ['audi', 'bmw', 'toyota']
if 'bmw' in cats:
print('bmw is in cats')
if 'toyota1' not in cats:
print('toyota1 is not in cats')
2. 条件表达式
语法：value_if_true if condition else value_if_false
比如 c = a if a > b else b, 先执行中间的( if a > b )，条件成立返回左边a，条件不成立返回右边 b
示例：
text = "Hello, World!"
length = len(text)
check = "long" if length > 10 else "short"
print(check)
2. 判断
2.1 判空 not
变量判 None
value = None
if not value:
print("Value is None")
字符串判空：
text = ""
if not text:
print("The string is empty")
列表判空：
numbers = []
if not numbers:
print("numbers is empty")
2.2 is not
is not 用于检查两个对象是否指向不同的内存位置
if a is not b:
...
检查对象是否为 None
if value is not None:
...
