operator module in Python

Posted by chunyang on November 2, 2019
TAGS: #python

Introduction

Python’s operator module provides us a lot of useful functions. We can write less lambda functions.

Common operator

  • add/sub/mul/floordiv/truediv
  • mod, imod
  • pow
  • neg, pos
  • abs

The i* is the corresponding part of swapping the arguments. For example if a + b fails due to the missing definition of operator + for a, Python will try to swap them and call b+a.

Relation

  • ge/gt
  • le/lt
  • eq/ne
  • not_
  • is_not
  • is_
  • truth

Bit operations

  • lshift, rshitf
  • xor
  • or_
  • and_
  • inv, invert

Elements and attributes

  • attrgetter
  • itemgetter
  • setitem(a, b, c): a[b] = c
  • delitem(a, b): del a[b]
  • contains(a, b): b in a

Other

  • countOf(a, b)
  • indexOf(a, b)
  • concat(a, b): a + b as sequence
  • methodcaller: return a callable object
    • methodcaller(a)(r) equals: r.a()
    • methodcaller(a, c, b=3)(r) equals: r.a(c, b=3)

Examples

import operator as op
# reduce an array

a = [1, 2, 3]
reduce(op.add, a, 0)

b = [[0, 1], [2, 3], [3, 4]]
reduce(op.add, map(op.itemgetter(0), b), 0)

b = [{"0": 1}, {"0": 3}, {"0": 4}]
reduce(op.add, map(op.itemgetter("0"), b), 0)

class A: pass
c = A()
c.a = 3
d = A()
d.a = 4
list(map(op.attrgetter("a"), [c, d]))


b = [{"0": 1}, {"0": 3}, {"1": 4}]
[op.contains("0", bb) for bb in b]
list(map(lambda x:op.contains(b, x), b))


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