python标准库介绍——8 operator 模块详解

==operator 模块==

``operator`` 模块为 Python 提供了一个 "功能性" 的标准操作符接口. 当使用 ``map`` 以及
``filter`` 一类的函数的时候, ``operator`` 模块中的函数可以替换一些 ``lambda`` 函式.
而且这些函数在一些喜欢写晦涩代码的程序员中很流行. [Example 1-62 #eg-1-62] 展示了
``operator`` 模块的一般用法.

====Example 1-62. 使用 operator 模块====[eg-1-62]

```
File: operator-example-1.py

import operator

sequence = 1, 2, 4

print "add", "=>", reduce(operator.add, sequence)
print "sub", "=>", reduce(operator.sub, sequence)
print "mul", "=>", reduce(operator.mul, sequence)
print "concat", "=>", operator.concat("spam", "egg")
print "repeat", "=>", operator.repeat("spam", 5)
print "getitem", "=>", operator.getitem(sequence, 2)
print "indexOf", "=>", operator.indexOf(sequence, 2)
print "sequenceIncludes", "=>", operator.sequenceIncludes(sequence, 3)

*B*add => 7
sub => -5
mul => 8
concat => spamegg
repeat => spamspamspamspamspam

getitem => 4
indexOf => 1
sequenceIncludes => 0*b*
```

[Example 1-63 #eg-1-63] 展示了一些可以用于检查对象类型的 ``operator`` 函数.

====Example 1-63. 使用 operator 模块检查类型====[eg-1-63]

```
File: operator-example-2.py

import operator
import UserList

def dump(data):
    print type(data), "=>",
    if operator.isCallable(data):
        print "CALLABLE",
    if operator.isMappingType(data):
        print "MAPPING",
    if operator.isNumberType(data):
        print "NUMBER",
    if operator.isSequenceType(data):
        print "SEQUENCE",
    print

dump(0)
dump("string")
dump("string"[0])
dump([1, 2, 3])
dump((1, 2, 3))
dump({"a": 1})
dump(len) # function 函数
dump(UserList) # module 模块
dump(UserList.UserList) # class 类
dump(UserList.UserList()) # instance 实例

*B*<type 'int'> => NUMBER
<type 'string'> => SEQUENCE
<type 'string'> => SEQUENCE
<type 'list'> => SEQUENCE
<type 'tuple'> => SEQUENCE
<type 'dictionary'> => MAPPING
<type 'builtin_function_or_method'> => CALLABLE
<type 'module'> =>
<type 'class'> => CALLABLE
<type 'instance'> => MAPPING NUMBER SEQUENCE*b*
```

这里需要注意 ``operator`` 模块使用非常规的方法处理对象实例. 所以使用
``isNumberType`` , ``isMappingType`` , 以及 ``isSequenceType`` 函数的时候要小心,
这很容易降低代码的扩展性.

同样需要注意的是一个字符串序列成员 (单个字符) 也是序列. 所以当在递归函数使用 isSequenceType 来截断对象树的时候, 别把普通字符串作为参数(或者是任何包含字符串的序列对象).