4. if 分支语句

1. 单分支

if condition:

statement1

statement2

2. 双分支

if condition:

statement1

statement2

else:

statement3

statement4

3. if else 嵌套

if condition:

statement1

statement2

else:

if condition2:

statement3

statement4

4. 条件判断表达式：

> < >= <= == != and or not