一、表达式
1.概念:运算符和操作数所构成的序列
In [18]:
a = [1,2,3]
a
Out[18]:
[1, 2, 3]
2.优先级
In [19]:
a,b,c = 1,2,3
In [20]:
a+b*c
Out[20]:
7
In [21]:
a or b and c
Out[21]:
1
and 优先级高于or.同级:从左到右(左结合),有赋值计算(右集合)
注意:自己写代码为了能够清晰表达意图,一定要加括号。
二、条件
1.普通判断
In [22]:
a = True
if a:
print("hello")
else:
print("world")
hello
2.表达式做判断
In [23]:
a = 1
b = 2
if a>b:
print("hello")
else:
print("world")
world
3.应用elif 减少嵌套
In [24]:
a = 3
if a == 1:
print("h")
elif a == 2:
print("e")
elif a == 3:
print("l")
else :
print("o")
l
三、循环
1.while循环
In [25]:
a = 1
while a < 6:
print(a)
a = a+1
else:
print("a=6")
1
2
3
4
5
a=6
2.for循环
In [26]:
for i in range(0,3):
print(i)
0
1
2
3.循环退出
3.1 continue 退出此次循环
In [27]:
a = 1
while a < 6:
a = a+1
if a ==4:
break
print(a)
else:
print("a=6")
2
3
3.2 break退出当前循环
In [28]:
a = 1
while a < 6:
a = a+1
if a ==4:
continue
print(a)
else:
print("a=6")
2
3
5
6
a=6