operator — Standard operators as functions¶
The 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) is equivalent to a < b , le(a, b) is equivalent to a b and ge(a, b) is equivalent to a >= b . Note that these functions can return any value, which may or may not be interpretable as a Boolean value. See Comparisons 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.)
Return True if obj is true, and False otherwise. This is equivalent to using the bool constructor.
Return a is b . Tests object identity.
Return a is not b . Tests object identity.
The mathematical and bitwise operations are the most numerous:
operator. abs ( obj ) ¶ operator. __abs__ ( obj ) ¶
Return the absolute value of obj.
operator. add ( a , b ) ¶ operator. __add__ ( a , b ) ¶
Return a + b , for a and b numbers.
operator. and_ ( a , b ) ¶ operator. __and__ ( a , b ) ¶
Return the bitwise and of a and b.
operator. floordiv ( a , b ) ¶ operator. __floordiv__ ( a , b ) ¶
operator. index ( a ) ¶ operator. __index__ ( a ) ¶
Return a converted to an integer. Equivalent to a.__index__() .
Changed in version 3.10: The result always has exact type int . Previously, the result could have been an instance of a subclass of int .
operator. inv ( obj ) ¶ operator. invert ( obj ) ¶ operator. __inv__ ( obj ) ¶ operator. __invert__ ( obj ) ¶
Return the bitwise inverse of the number obj. This is equivalent to ~obj .
operator. lshift ( a , b ) ¶ operator. __lshift__ ( a , b ) ¶
Return a shifted left by b.
operator. mod ( a , b ) ¶ operator. __mod__ ( a , b ) ¶
operator. mul ( a , b ) ¶ operator. __mul__ ( a , b ) ¶
Return a * b , for a and b numbers.
operator. matmul ( a , b ) ¶ operator. __matmul__ ( a , b ) ¶
operator. or_ ( a , b ) ¶ operator. __or__ ( a , b ) ¶
Return the bitwise or of a and b.
operator. pos ( obj ) ¶ operator. __pos__ ( obj ) ¶
operator. pow ( a , b ) ¶ operator. __pow__ ( a , b ) ¶
Return a ** b , for a and b numbers.
operator. rshift ( a , b ) ¶ operator. __rshift__ ( a , b ) ¶
Return a shifted right by b.
operator. sub ( a , b ) ¶ operator. __sub__ ( a , b ) ¶
operator. truediv ( a , b ) ¶ operator. __truediv__ ( a , b ) ¶
Return 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. concat ( a , b ) ¶ operator. __concat__ ( a , b ) ¶
Return a + b for a and b sequences.
operator. contains ( a , b ) ¶ operator. __contains__ ( a , b ) ¶
Return the outcome of the test b in a . Note the reversed operands.
Return the number of occurrences of b in a.
operator. delitem ( a , b ) ¶ operator. __delitem__ ( a , b ) ¶
Remove the value of a at index b.
operator. getitem ( a , b ) ¶ operator. __getitem__ ( a , b ) ¶
Return the value of a at index 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 obj. First try to return its actual length, then an estimate using object.__length_hint__() , and finally return the default value.
The following operation works with callables:
operator. call ( obj , / , * args , ** kwargs ) ¶ operator. __call__ ( obj , / , * args , ** kwargs ) ¶
The 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:
- After f = attrgetter(‘name’) , the call f(b) returns b.name .
- After f = attrgetter(‘name’, ‘date’) , the call f(b) returns (b.name, b.date) .
- After f = attrgetter(‘name.first’, ‘name.last’) , the call f(b) returns (b.name.first, b.name.last) .
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
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:
- After f = itemgetter(2) , the call f(r) returns r[2] .
- After g = itemgetter(2, 5, 3) , the call g(r) returns (r[2], r[5], r[3]) .
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' >>> soldier = dict(rank='captain', name='dotterbart') >>> itemgetter('rank')(soldier) 'captain'
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)]
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:
- After f = methodcaller(‘name’) , the call f(b) returns b.name() .
- After f = methodcaller(‘name’, ‘foo’, bar=1) , the call f(b) returns b.name(‘foo’, bar=1) .
def methodcaller(name, /, *args, **kwargs): def caller(obj): return getattr(obj, name)(*args, **kwargs) return caller
Mapping Operators to Functions¶
This table shows how abstract operations correspond to operator symbols in the Python syntax and the functions in the operator module.
Basic Python Semantics: Operators
In the previous section, we began to look at the semantics of Python variables and objects; here we’ll dig into the semantics of the various operators included in the language. By the end of this section, you’ll have the basic tools to begin comparing and operating on data in Python.
Arithmetic Operations¶
Python implements seven basic binary arithmetic operators, two of which can double as unary operators. They are summarized in the following table:
| Operator | Name | Description |
|---|---|---|
| a + b | Addition | Sum of a and b |
| a — b | Subtraction | Difference of a and b |
| a * b | Multiplication | Product of a and b |
| a / b | True division | Quotient of a and b |
| a // b | Floor division | Quotient of a and b , removing fractional parts |
| a % b | Modulus | Integer remainder after division of a by b |
| a ** b | Exponentiation | a raised to the power of b |
| -a | Negation | The negative of a |
| +a | Unary plus | a unchanged (rarely used) |
These operators can be used and combined in intuitive ways, using standard parentheses to group operations. For example:
# addition, subtraction, multiplication (4 + 8) * (6.5 - 3)
Floor division is true division with fractional parts truncated:
# Floor division print(11 // 2)
The floor division operator was added in Python 3; you should be aware if working in Python 2 that the standard division operator ( / ) acts like floor division for integers and like true division for floating-point numbers.
Finally, I’ll mention an eighth arithmetic operator that was added in Python 3.5: the a @ b operator, which is meant to indicate the matrix product of a and b , for use in various linear algebra packages.
Bitwise Operations¶
In addition to the standard numerical operations, Python includes operators to perform bitwise logical operations on integers. These are much less commonly used than the standard arithmetic operations, but it’s useful to know that they exist. The six bitwise operators are summarized in the following table:
| Operator | Name | Description |
|---|---|---|
| a & b | Bitwise AND | Bits defined in both a and b |
| a | b | Bitwise OR | Bits defined in a or b or both |
| a ^ b | Bitwise XOR | Bits defined in a or b but not both |
| a | Bit shift left | Shift bits of a left by b units |
| a >> b | Bit shift right | Shift bits of a right by b units |
| ~a | Bitwise NOT | Bitwise negation of a |
These bitwise operators only make sense in terms of the binary representation of numbers, which you can see using the built-in bin function: