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。
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
#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
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
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]
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']
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)]
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)