The operator module exports a set of functions implemented in C corresponding to the intrinsic operators of Python. For example, operator.add(x, y) is equivalent to the expression x+y. The function names are those used for special class methods; variants without leading and trailing __ are also provided for convenience.
The functions fall into categories that perform object comparisons, logical operations, mathematical operations, sequence operations, and abstract type tests.
The object comparison functions are useful for all objects, and are named after the rich comparison operators they support:
The logical operations are also generally applicable to all objects, and support truth tests, identity tests, and boolean operations:
The mathematical and bitwise operations are the most numerous:
Operations which work with sequences include:
Many operations have an “in-place” version. The following functions provide a more primitive access to in-place operators than the usual syntax does; for example, the statement x += y is equivalent to 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.
The operator module also defines a few predicates to test the type of objects.
Note
Be careful not to misinterpret the results of these functions; none have any measure of reliability with instance objects. For example:
>>> class C:
... pass
...
>>> import operator
>>> obj = C()
>>> operator.isMappingType(obj)
True
Note
Since there are now abstract classes for collection types, you should write, for example, isinstance(obj, collections.Mapping) and isinstance(obj, collections.Sequence).
Returns true if the object obj supports the mapping interface. This is true for dictionaries and all instance objects defining __getitem__().
Warning
There is no reliable way to test if an instance supports the complete mapping protocol since the interface itself is ill-defined. This makes this test less useful than it otherwise might be.
Returns true if the object obj represents a number. This is true for all numeric types implemented in C.
Warning
There is no reliable way to test if an instance supports the complete numeric interface since the interface itself is ill-defined. This makes this test less useful than it otherwise might be.
Returns true if the object obj supports the sequence protocol. This returns true for all objects which define sequence methods in C, and for all instance objects defining __getitem__().
Warning
There is no reliable way to test if an instance supports the complete sequence interface since the interface itself is ill-defined. This makes this test less useful than it otherwise might be.
Example: Build a dictionary that maps the ordinals from 0 to 255 to their character equivalents.
>>> d = {}
>>> keys = range(256)
>>> vals = map(chr, keys)
>>> map(operator.setitem, [d]*len(keys), keys, vals) # doctest: +SKIP
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.
Return a callable object that fetches attr from its operand. If more than one attribute is requested, returns a tuple of attributes. 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).
The attribute names can also contain dots; after f = attrgetter('date.month'), the call f(b) returns b.date.month.
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. Equivalent to:
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)
>>> map(getcount, inventory)
[3, 2, 5, 1]
>>> sorted(inventory, key=getcount)
[('orange', 1), ('banana', 2), ('apple', 3), ('pear', 5)]
This table shows how abstract operations correspond to operator symbols in the Python syntax and the functions in the operator module.
| Operation | Syntax | 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) |
| Indexing | obj[k] | getitem(obj, k) |
| Left Shift | a << b | lshift(a, b) |
| Modulo | a % b | mod(a, b) |
| Multiplication | a * b | mul(a, b) |
| Negation (Arithmetic) | - a | neg(a) |
| Negation (Logical) | not a | not_(a) |
| Right Shift | a >> b | rshift(a, b) |
| Sequence Repetition | seq * i | repeat(seq, i) |
| 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) |