Stats

Contributors: 3
2016-07-23
Licensed under: CC-BY-SA

Not affiliated with Stack Overflow
Rip Tutorial: info@zzzprojects.com

Download eBook

Exponentiation using builtins: ** and pow()

Download python eBook

Example

Exponentiation can be used by using the builtin pow-function or the ** operator:

2 ** 3    # 8
pow(2, 3) # 8

For most (all in Python 2.x) arithmetic operations the result's type will be that of the wider operand. This is not true for **; the following cases are exceptions from this rule:

  • Base: int, exponent: int < 0:

    2 ** -3
    # Out: 0.125 (result is a float)
    
  • This is also valid for Python 3.x.

  • Before Python 2.2.0, this raised a ValueError.

  • Base: int < 0 or float < 0, exponent: float != int

    (-2) ** (0.5)  # also (-2.) ** (0.5)    
    # Out: (8.659560562354934e-17+1.4142135623730951j) (result is complex)
    
  • Before python 3.0.0, this raised a ValueError.

The operator module contains two functions that are equivalent to the **-operator:

import operator
operator.pow(4, 2)      # 16
operator.__pow__(4, 3)  # 64

or one could directly call the __pow__ method:

val1, val2 = 4, 2
val1.__pow__(val2)      # 16
val2.__rpow__(val1)     # 16
# in-place power operation isn't supported by immutable classes like int, float, complex:
# val1.__ipow__(val2)