power arguments in Python

Question

Undertaking a task to Write a function power that accepts two arguments, a and b and calculates a raised to the power b.

Example

power(2, 3) => 8

Note: Don't use

2 ** 3

and don't use

Math.pow(2, 3)

I have tried this

def power(a,b): return eval(((str(a)+"*")*b)[:-1])

And it works but seems to fail one test which is to return_1_when_exp_is_0

and i also get the error

Unhandled Exception: unexpected EOF while parsing (, line 0)

Please how do i solve this issue considering that i am new to python

if-else: if exp is 0, return 1 else return the result of a calculation. You do not need to resort to using eval, either. — Tom Lynch
– Tom Lynch, Commented May 21, 2017 at 2:00
@TomLynch i fill bad right now. Considered that but did it wrong thanks a lot — diagold
– diagold, Commented May 21, 2017 at 2:13

diagold · Accepted Answer · 2017-05-21 02:18:54Z

0

This worked fine

def power(a,b): if b == 0: return 1 else: return eval(((str(a)+"*")*b)[:-1])

answered May 21, 2017 at 2:18

diagold

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1 Comment

okainov Over a year ago

You should not use eval without explicit reason. Especially for pure math\algorithm task. Basically what you do here is just performing b-1 multiplications.

AChampion · Accepted Answer · 2017-05-21 02:30:48Z

Using eval is a terrible idea, but if you really wanted to then using join() would be a better way to create the string:

def power(a, b): return eval('*'.join([str(a)]*b)) >>> power(2, 3) 8

If you add ['1'] to the front then the 0 exponent behaves properly:

def power(a, b): return eval('*'.join(['1']+[str(a)]*b)) >>> power(2, 0) 1

However, this is simple to implement for integer exponents with a for loop:

def power(n, e): t = 1 for _ in range(e): t *= n return t >>> power(2, 3) 8 >>> power(2, 0) 1

You could also use functools.reduce() to do the same thing:

import functools as ft import operator as op def power(n, e): return ft.reduce(op.mul, [n]*e, 1)

Hisham Sliman · Accepted Answer · 2017-05-22 22:50:12Z

0

You can use a for loop

x=1 for i in range(b): x=x*a print(x)

edited May 22, 2017 at 22:50

answered May 21, 2017 at 2:12

Hisham Sliman

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1 Comment

AChampion Over a year ago

a=2, b=3 prints 16 not 8... I'm sure you meant to initialize x=1. Setting x=1 also solves the 0 exponent ask, a=<anything>.b=0 will print 1.

Mwangi Thiga · Accepted Answer · 2018-04-08 20:53:13Z

def power(theNumber, thePower): #basically, multiply the number for power times try: theNumber=int(theNumber) thePower=int(thePower) if theNumber == 0: return 0 elif thePower == 0: return 1 else: return theNumber * power(theNumber,thePower-1) except exception as err: return 'Only digits are allowed as input'

okainov · Accepted Answer · 2018-10-30 20:24:27Z

You should avoid eval by all costs, especially when it's very simple to implement pure algorithmic efficient solution. Classic efficient algorithm is Exponentiation_by_squaring. Instead of computing and multiplying numbers n times, you can always divide it to squares to archive logarithmic* complexity. For example, for calculating x^15:

x^15 = (x^7)*(x^7)*x x^7 = (x^3)*(x^3)*x x^3 = x*x*x

Thus taking 6 multiplications instead of 14.

def pow3(x, n): r = 1 while n: if n % 2 == 1: r *= x n -= 1 x *= x n /= 2 return r

Source: https://helloacm.com/exponentiation-by-squaring/

Note: it was not mentioned in the question, but everything above considers N to be positive integer. If your question was also covering fractional or negative exponent, suggested approach will not work "as is".

* Of course depends on length of x and complexity of multiplying, see Wikipedia for detailed complexity analysis.

Also may be interesting to check out following questions: C solution or Python implementing pow() for exponentiation by squaring for very large integers

Madhur Bhaiya · Accepted Answer · 2018-10-30 19:42:00Z

-1

def power(a, b): if b == 0: return 1 else: return a ** b

edited Oct 30, 2018 at 19:42

Madhur Bhaiya

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answered Oct 30, 2018 at 19:35

Ace

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2 Comments

Madhur Bhaiya Over a year ago

Code only answers are not considered good. Please add some explanation to it.

okainov Over a year ago

This does not answer the question, because it was explicitly mentioned in the text "do not use **"

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