operator — Built-in Operators的函数接口

翻译自：https://pymotw.com/3/operator/index.html

在使用iterators有时会需要一些函数表达式，通常可使用lambda函数来实现，但operator 模块中定义了不少于与built-in operations 相对应的算数，比较函数，在operator 中定义的这些常用操作就可以不用自己去定义，直接拿来用。

逻辑操作

from operator import *

a = -1
b = 5

print('a =', a)
print('b =', b)
print()

print('not_(a)     :', not_(a))  #对应not a
print('truth(a)    :', truth(a))  #对应a
print('is_(a, b)   :', is_(a, b))  #对应a is b
print('is_not(a, b):', is_not(a, b))   #对应a is not b

##结果
a = -1
b = 5

not_(a)     : False
truth(a)    : True
is_(a, b)   : False
is_not(a, b): True

比较操作

#lt(<)   le(<=)  eq(=)  ne(!=)  ge(>=)  gt(>)
from operator import *

a = 1
b = 5.0

print('a =', a)
print('b =', b)
for func in (lt, le, eq, ne, ge, gt):
    print('{}(a, b): {}'.format(func.__name__, func(a, b)))

#结果
a = 1
b = 5.0
lt(a, b): True
le(a, b): True
eq(a, b): False
ne(a, b): True
ge(a, b): False
gt(a, b): False

算术操作

from operator import *

a = -1
b = 5.0
c = 2
d = 6

print('a =', a)
print('b =', b)
print('c =', c)
print('d =', d)

print('\nPositive/Negative:')
print('abs(a):', abs(a))
print('neg(a):', neg(a))
print('neg(b):', neg(b))
print('pos(a):', pos(a))
print('pos(b):', pos(b))

print('\nArithmetic:')
print('add(a, b)     :', add(a, b))
print('floordiv(a, b):', floordiv(a, b))  #整数相除
print('floordiv(d, c):', floordiv(d, c))
print('mod(a, b)     :', mod(a, b))
print('mul(a, b)     :', mul(a, b))
print('pow(c, d)     :', pow(c, d))
print('sub(b, a)     :', sub(b, a))
print('truediv(a, b) :', truediv(a, b))   #浮点数相除
print('truediv(d, c) :', truediv(d, c))

print('\nBitwise:')
print('and_(c, d)  :', and_(c, d))
print('invert(c)   :', invert(c))
print('lshift(c, d):', lshift(c, d))
print('or_(c, d)   :', or_(c, d))
print('rshift(d, c):', rshift(d, c))
print('xor(c, d)   :', xor(c, d))

#结果
a = -1
b = 5.0
c = 2
d = 6

Positive/Negative:
abs(a): 1
neg(a): 1
neg(b): -5.0
pos(a): -1
pos(b): 5.0

Arithmetic:
add(a, b)     : 4.0
floordiv(a, b): -1.0
floordiv(d, c): 3
mod(a, b)     : 4.0
mul(a, b)     : -5.0
pow(c, d)     : 64
sub(b, a)     : 6.0
truediv(a, b) : -0.2
truediv(d, c) : 3.0

Bitwise:
and_(c, d)  : 2
invert(c)   : -3
lshift(c, d): 128
or_(c, d)   : 6
rshift(d, c): 1
xor(c, d)   : 4

序列操作

基本可分为4大类：构建序列、查找元素、获取内容、删除元素

from operator import *

a = [1, 2, 3]
b = ['a', 'b', 'c']

print('a =', a)
print('b =', b)

print('\nConstructive:')
print('  concat(a, b):', concat(a, b))

print('\nSearching:')
print('  contains(a, 1)  :', contains(a, 1))
print('  contains(b, "d"):', contains(b, "d"))
print('  countOf(a, 1)   :', countOf(a, 1))
print('  countOf(b, "d") :', countOf(b, "d"))
print('  indexOf(a, 5)   :', indexOf(a, 1))

print('\nAccess Items:')
print('  getitem(b, 1)                  :',
      getitem(b, 1))
print('  getitem(b, slice(1, 3))        :',
      getitem(b, slice(1, 3)))
print('  setitem(b, 1, "d")             :', end=' ')
setitem(b, 1, "d")
print(b)
print('  setitem(a, slice(1, 3), [4, 5]):', end=' ')
setitem(a, slice(1, 3), [4, 5])
print(a)

print('\nDestructive:')
print('  delitem(b, 1)          :', end=' ')
delitem(b, 1)
print(b)
print('  delitem(a, slice(1, 3)):', end=' ')
delitem(a, slice(1, 3))
print(a)

#结果
a = [1, 2, 3]
b = ['a', 'b', 'c']

Constructive:
  concat(a, b): [1, 2, 3, 'a', 'b', 'c']

Searching:
  contains(a, 1)  : True
  contains(b, "d"): False
  countOf(a, 1)   : 1
  countOf(b, "d") : 0
  indexOf(a, 5)   : 0

Access Items:
  getitem(b, 1)                  : b
  getitem(b, slice(1, 3))        : ['b', 'c']
  setitem(b, 1, "d")             : ['a', 'd', 'c']
  setitem(a, slice(1, 3), [4, 5]): [1, 4, 5]

Destructive:
  delitem(b, 1)          : ['a', 'c']
  delitem(a, slice(1, 3)): [1]

in-place 操作符

from operator import *

a = -1
b = 5.0
c = [1, 2, 3]
d = ['a', 'b', 'c']
print('a =', a)
print('b =', b)
print('c =', c)
print('d =', d)
print()

a = iadd(a, b)
print('a = iadd(a, b) =>', a)
print()

c = iconcat(c, d)
print('c = iconcat(c, d) =>', c)

#结果
a = -1
b = 5.0
c = [1, 2, 3]
d = ['a', 'b', 'c']

a = iadd(a, b) => 4.0

c = iconcat(c, d) => [1, 2, 3, 'a', 'b', 'c']

Attribute and Item “Getters”

operator中的getters是非常有用的操作， 避免了在使用iterator时写lambda函数的麻烦
Attribute getters等同于lambda x, n=’attrname’: getattr(x, n):
Item getters等同于 lambda x, y=5: x[y]:

# Attribute getters例子
from operator import *


class MyObj:
    """example class for attrgetter"""

    def __init__(self, arg):
        super().__init__()
        self.arg = arg

    def __repr__(self):
        return 'MyObj({})'.format(self.arg)


l = [MyObj(i) for i in range(5)]
print('objects   :', l)

# Extract the 'arg' value from each object
g = attrgetter('arg')
vals = [g(i) for i in l]
print('arg values:', vals)

l.reverse()  
print('reversed  :', l)
# Sort using arg
print('sorted    :', sorted(l, key=g))  #sorted python內建函数，对有可迭代的对象进行排序操作，这里sorted逻辑相当于sorted(l, key=lamda x,n = 'arg': getattr(x,n))

#结果
objects   : [MyObj(0), MyObj(1), MyObj(2), MyObj(3), MyObj(4)]
arg values: [0, 1, 2, 3, 4]
reversed  : [MyObj(4), MyObj(3), MyObj(2), MyObj(1), MyObj(0)]
sorted    : [MyObj(0), MyObj(1), MyObj(2), MyObj(3), MyObj(4)]

#Item getters例子
from operator import *

l = [dict(val=-1 * i) for i in range(4)]
print('Dictionaries:')
print(' original:', l)
g = itemgetter('val')
vals = [g(i) for i in l]
print('   values:', vals)
print('   sorted:', sorted(l, key=g))  #相当于 sorted(l, key=lamda x, y='val': x[y])

print()
l = [(i, i * -2) for i in range(4)]
print('\nTuples:')
print(' original:', l)
g = itemgetter(1)
vals = [g(i) for i in l]
print('   values:', vals)
print('   sorted:', sorted(l, key=g))  #相当于 sorted(l, key=lamda x, y=1: x[y])

#结果
Dictionaries:
 original: [{'val': 0}, {'val': -1}, {'val': -2}, {'val': -3}]
   values: [0, -1, -2, -3]
   sorted: [{'val': -3}, {'val': -2}, {'val': -1}, {'val': 0}]


Tuples:
 original: [(0, 0), (1, -2), (2, -4), (3, -6)]
   values: [0, -2, -4, -6]
   sorted: [(3, -6), (2, -4), (1, -2), (0, 0)]

operator 模块中的方法同样适用于类

from operator import *


class MyObj:
    """Example for operator overloading"""

    def __init__(self, val):
        super(MyObj, self).__init__()
        self.val = val

    def __str__(self):
        return 'MyObj({})'.format(self.val)

    def __lt__(self, other):
        """compare for less-than"""
        print('Testing {} < {}'.format(self, other))
        return self.val < other.val

    def __add__(self, other):
        """add values"""
        print('Adding {} + {}'.format(self, other))
        return MyObj(self.val + other.val)


a = MyObj(1)
b = MyObj(2)

print('Comparison:')
print(lt(a, b))

print('\nArithmetic:')
print(add(a, b))

#结果
Comparison:
Testing MyObj(1) < MyObj(2)
True

Arithmetic:
Adding MyObj(1) + MyObj(2)
MyObj(3)