英文文档：

chr(i)
Return the string representing a character whose Unicode code point is the integer i. For example, chr(97) returns the string 'a', whilechr(8364) returns the string '€'. This is the inverse of ord().
The valid range for the argument is from 0 through 1,114,111 (0x10FFFF in base 16). ValueError will be raised if i is outside that range

说明：

1.函数返回整形参数值所对应的Unicode字符的字符串表示

>>> chr(97) #参数类型为整数
'a'
>>> chr('97') #参数传入字符串时报错
Traceback (most recent call last): 
  File "<pyshell#6>", line 1, in <module> 
chr('97')
TypeError: an integer is required (got type str)
>>> type(chr(97)) #返回类型为字符串
<class 'str'>

2.它的功能与ord函数刚好相反

>>> chr(97)
'a'
>>> ord('a')
97

3.传入的参数值范围必须在0-1114111(十六进制为0x10FFFF)之间，否则将报ValueError错误

>>> chr(-1) #小于0报错
Traceback (most recent call last): 
  File "<pyshell#10>", line 1, in <module> 
    chr(-1)
ValueError: chr() arg not in range(0x110000)
>>> chr(1114111)
'\U0010ffff'
>>> chr(1114112) #超过1114111报错
Traceback (most recent call last): 
  File "<pyshell#13>", line 1, in <module> 
    chr(1114112)
ValueError: chr() arg not in range(0x110000)