operator
— 作为函数的标准运算符
¶
源代码： Lib/operator.py
operator
module exports a set of efficient functions corresponding to the intrinsic operators of Python. For example,
operator.add(x,
y)
is equivalent to the expression
x+y
. Many function names are those used for special methods, without the double underscores. For backward compatibility, many of these have a variant with the double underscores kept. The variants without the double underscores are preferred for clarity.
The functions fall into categories that perform object comparisons, logical operations, mathematical operations and sequence operations.
The object comparison functions are useful for all objects, and are named after the rich comparison operators they support:
operator.
lt
(
a
,
b
)
¶
operator.
le
(
a
,
b
)
¶
operator.
eq
(
a
,
b
)
¶
operator.
ne
(
a
,
b
)
¶
operator.
ge
(
a
,
b
)
¶
operator.
gt
(
a
,
b
)
¶
operator.
__lt__
(
a
,
b
)
¶
operator.
__le__
(
a
,
b
)
¶
operator.
__eq__
(
a
,
b
)
¶
operator.
__ne__
(
a
,
b
)
¶
operator.
__ge__
(
a
,
b
)
¶
operator.
__gt__
(
a
,
b
)
¶
Perform “rich comparisons” between
a
and
b
. Specifically,
lt(a,
b)
相当于
a
<
b
,
le(a,
b)
相当于
a
<=
b
,
eq(a,
b)
相当于
a
==
b
,
ne(a,
b)
相当于
a
!=
b
,
gt(a,
b)
相当于
a
>
b
and
ge(a,
b)
相当于
a
>=
b
. Note that these functions can return any value, which may or may not be interpretable as a Boolean value. See
比较
for more information about rich comparisons.
The logical operations are also generally applicable to all objects, and support truth tests, identity tests, and boolean operations:
operator.
not_
(
obj
)
¶
operator.
__not__
(
obj
)
¶
Return the outcome of
not
obj
. (Note that there is no
__not__()
method for object instances; only the interpreter core defines this operation. The result is affected by the
__bool__()
and
__len__()
methods.)
operator.
is_
(
a
,
b
)
¶
返回
a
is
b
。测试对象标识。
operator.
is_not
(
a
,
b
)
¶
返回
a
is
not
b
。测试对象标识。
The mathematical and bitwise operations are the most numerous:
operator.
index
(
a
)
¶
operator.
__index__
(
a
)
¶
返回
a
converted to an integer. Equivalent to
a.__index__()
.
operator.
inv
(
obj
)
¶
operator.
invert
(
obj
)
¶
operator.
__inv__
(
obj
)
¶
operator.
__invert__
(
obj
)
¶
Return the bitwise inverse of the number
obj
。这相当于
~obj
.
operator.
truediv
(
a
,
b
)
¶
operator.
__truediv__
(
a
,
b
)
¶
返回
a
/
b
where 2/3 is .66 rather than 0. This is also known as “true” division.
operator.
xor
(
a
,
b
)
¶
operator.
__xor__
(
a
,
b
)
¶
Return the bitwise exclusive or of a and b .
Operations which work with sequences (some of them with mappings too) include:
operator.
contains
(
a
,
b
)
¶
operator.
__contains__
(
a
,
b
)
¶
Return the outcome of the test
b
in
a
. Note the reversed operands.
operator.
countOf
(
a
,
b
)
¶
Return the number of occurrences of b in a .
operator.
indexOf
(
a
,
b
)
¶
Return the index of the first of occurrence of b in a .
operator.
setitem
(
a
,
b
,
c
)
¶
operator.
__setitem__
(
a
,
b
,
c
)
¶
Set the value of a at index b to c .
operator.
length_hint
(
obj
,
default=0
)
¶
Return an estimated length for the object
o
. First try to return its actual length, then an estimate using
object.__length_hint__()
, and finally return the default value.
3.4 版新增。
operator
module also defines tools for generalized attribute and item lookups. These are useful for making fast field extractors as arguments for
map()
,
sorted()
,
itertools.groupby()
, or other functions that expect a function argument.
operator.
attrgetter
(
attr
)
¶
operator.
attrgetter
(
*attrs
)
Return a callable object that fetches attr from its operand. If more than one attribute is requested, returns a tuple of attributes. The attribute names can also contain dots. For example:
f
=
attrgetter('name')
, the call
f(b)
返回
b.name
.
f
=
attrgetter('name',
'date')
, the call
f(b)
返回
(b.name,
b.date)
.
f
=
attrgetter('name.first',
'name.last')
, the call
f(b)
返回
(b.name.first,
b.name.last)
.
等效于：
def attrgetter(*items):
if any(not isinstance(item, str) for item in items):
raise TypeError('attribute name must be a string')
if len(items) == 1:
attr = items[0]
def g(obj):
return resolve_attr(obj, attr)
else:
def g(obj):
return tuple(resolve_attr(obj, attr) for attr in items)
return g
def resolve_attr(obj, attr):
for name in attr.split("."):
obj = getattr(obj, name)
return obj
operator.
itemgetter
(
item
)
¶
operator.
itemgetter
(
*items
)
Return a callable object that fetches
item
from its operand using the operand’s
__getitem__()
method. If multiple items are specified, returns a tuple of lookup values. For example:
f
=
itemgetter(2)
, the call
f(r)
返回
r[2]
.
g
=
itemgetter(2,
5,
3)
, the call
g(r)
返回
(r[2],
r[5],
r[3])
.
等效于：
def itemgetter(*items):
if len(items) == 1:
item = items[0]
def g(obj):
return obj[item]
else:
def g(obj):
return tuple(obj[item] for item in items)
return g
The items can be any type accepted by the operand’s
__getitem__()
method. Dictionaries accept any hashable value. Lists, tuples, and strings accept an index or a slice:
>>> itemgetter(1)('ABCDEFG')
'B'
>>> itemgetter(1,3,5)('ABCDEFG')
('B', 'D', 'F')
>>> itemgetter(slice(2,None))('ABCDEFG')
'CDEFG'
Example of using
itemgetter()
to retrieve specific fields from a tuple record:
>>> inventory = [('apple', 3), ('banana', 2), ('pear', 5), ('orange', 1)]
>>> getcount = itemgetter(1)
>>> list(map(getcount, inventory))
[3, 2, 5, 1]
>>> sorted(inventory, key=getcount)
[('orange', 1), ('banana', 2), ('apple', 3), ('pear', 5)]
operator.
methodcaller
(
name
[
,
args...
]
)
¶
Return a callable object that calls the method name on its operand. If additional arguments and/or keyword arguments are given, they will be given to the method as well. For example:
f
=
methodcaller('name')
, the call
f(b)
返回
b.name()
.
f
=
methodcaller('name',
'foo',
bar=1)
, the call
f(b)
返回
b.name('foo',
bar=1)
.
等效于：
def methodcaller(name, *args, **kwargs):
def caller(obj):
return getattr(obj, name)(*args, **kwargs)
return caller
This table shows how abstract operations correspond to operator symbols in the Python syntax and the functions in the
operator
模块。
| 操作 | 句法 | Function |
|---|---|---|
| Addition |
a
+
b
|
add(a,
b)
|
| Concatenation |
seq1
+
seq2
|
concat(seq1,
seq2)
|
| Containment Test |
obj
in
seq
|
contains(seq,
obj)
|
| Division |
a
/
b
|
truediv(a,
b)
|
| Division |
a
//
b
|
floordiv(a,
b)
|
| Bitwise And |
a
&
b
|
and_(a,
b)
|
| Bitwise Exclusive Or |
a
^
b
|
xor(a,
b)
|
| Bitwise Inversion |
~
a
|
invert(a)
|
| Bitwise Or |
a
|
b
|
or_(a,
b)
|
| Exponentiation |
a
**
b
|
pow(a,
b)
|
| Identity |
a
is
b
|
is_(a,
b)
|
| Identity |
a
is
not
b
|
is_not(a,
b)
|
| Indexed Assignment |
obj[k]
=
v
|
setitem(obj,
k,
v)
|
| Indexed Deletion |
del
obj[k]
|
delitem(obj,
k)
|
| 索引 |
obj[k]
|
getitem(obj,
k)
|
| Left Shift |
a
<<
b
|
lshift(a,
b)
|
| Modulo |
a
%
b
|
mod(a,
b)
|
| Multiplication |
a
*
b
|
mul(a,
b)
|
| Matrix Multiplication |
a
@
b
|
matmul(a,
b)
|
| Negation (Arithmetic) |
-
a
|
neg(a)
|
| Negation (Logical) |
not
a
|
not_(a)
|
| Positive |
+
a
|
pos(a)
|
| Right Shift |
a
>>
b
|
rshift(a,
b)
|
| Slice Assignment |
seq[i:j]
=
values
|
setitem(seq,
slice(i,
j),
values)
|
| Slice Deletion |
del
seq[i:j]
|
delitem(seq,
slice(i,
j))
|
| Slicing |
seq[i:j]
|
getitem(seq,
slice(i,
j))
|
| String Formatting |
s
%
obj
|
mod(s,
obj)
|
| Subtraction |
a
-
b
|
sub(a,
b)
|
| Truth Test |
obj
|
truth(obj)
|
| Ordering |
a
<
b
|
lt(a,
b)
|
| Ordering |
a
<=
b
|
le(a,
b)
|
| Equality |
a
==
b
|
eq(a,
b)
|
| Difference |
a
!=
b
|
ne(a,
b)
|
| Ordering |
a
>=
b
|
ge(a,
b)
|
| Ordering |
a
>
b
|
gt(a,
b)
|
Many operations have an “in-place” version. Listed below are functions providing a more primitive access to in-place operators than the usual syntax does; for example, the
语句
x
+=
y
相当于
x
=
operator.iadd(x,
y)
. Another way to put it is to say that
z
=
operator.iadd(x,
y)
is equivalent to the compound statement
z
=
x;
z
+=
y
.
In those examples, note that when an in-place method is called, the computation and assignment are performed in two separate steps. The in-place functions listed below only do the first step, calling the in-place method. The second step, assignment, is not handled.
For immutable targets such as strings, numbers, and tuples, the updated value is computed, but not assigned back to the input variable:
>>> a = 'hello'
>>> iadd(a, ' world')
'hello world'
>>> a
'hello'
For mutable targets such as lists and dictionaries, the inplace method will perform the update, so no subsequent assignment is necessary:
>>> s = ['h', 'e', 'l', 'l', 'o']
>>> iadd(s, [' ', 'w', 'o', 'r', 'l', 'd'])
['h', 'e', 'l', 'l', 'o', ' ', 'w', 'o', 'r', 'l', 'd']
>>> s
['h', 'e', 'l', 'l', 'o', ' ', 'w', 'o', 'r', 'l', 'd']
operator.
iconcat
(
a
,
b
)
¶
operator.
__iconcat__
(
a
,
b
)
¶
a
=
iconcat(a,
b)
相当于
a
+=
b
for
a
and
b
sequences.
operator.
ifloordiv
(
a
,
b
)
¶
operator.
__ifloordiv__
(
a
,
b
)
¶
a
=
ifloordiv(a,
b)
相当于
a
//=
b
.