类型判断和强制转化

Checking the Type

单 词	意思	音 标
floor operation	向下取整
mutable	可变的	/ˈmjuːtəb(ə)l/
immutable	不可变的	/ɪˈmjuːtəb(ə)l/
assignment	赋值

函数	例子	注意事项
Checking the Type	x=5 type(x) int	We can’t concatenate a string and a number…and we shouldn’t be able
Converting Types	x=3.3 int_y=int(x) type(int_y)	int() is one way to perform a floor operation
Why the Type Matters	float_x=5.5 string_y="5" float_x+float(string_y) 10.5 string_y+str(float_x) 55.5

Mutable or Immutable

函数	例子	输出
Mutable	Can be changed once created –  a list L can have its first element replaced.
Immutable	Can’t be changed once creating – a string S cannot have its first letter changed.
String = Immutable	name="LiQing" name[0]="Q"	TypeError: ‘str’ object does not support item assignment
if you want to change	name="LiQing" new_name="Q"+name[1:] new_name	‘QiQing’
Lists = Mutable	L=["1","2","3"] L[0]=100 L	输出结果 [100, ‘2’, ‘3’]
Numbers = Immutable