What is Python ord()? What is the use of ord()?

1 >>> ord("a")
2 97
3 >>> chr(97)
4 'a'

>>> [chr(i) for i in range(97,123)]
['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 
'm', 'n', 'o', 'p','q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']

# 用户输入字符
c = input("请输入一个字符: ")
 
# 用户输入ASCII码，并将输入的数字转为整型
a = int(input("请输入一个ASCII码: "))

print( c + " 的ASCII 码为", ord(c))
print( a , " 对应的字符为", chr(a))

1 请输入一个字符: a
2 请输入一个ASCII码: 101
3 a 的ASCII 码为 97
4 101  对应的字符为 e

>>> chr(65)
'A'
>>> ord('a')
97
>>> unichr(12345)
u'\u3039'
>>> chr(12345)
Traceback (most recent call last):
   File "<stdin>", line 1, in ?    
     chr(12345)
ValueError: chr() arg not in range(256)
>>> ord(u&#39;\ufffff&#39;)
Traceback (most recent call last):
   File "<stdin>", line 1, in ?
     ord(u&#39;\ufffff&#39;)
TypeError: ord() expected a character, but string of length 2 found
>>> ord(u&#39;\u2345&#39;)
9029