freecodecamp--freecodecamp/curriculum/challenges/english/blocks/daily-coding-challenges-python/68b7cadffed0e75a517da673.md

id, title, challengeType, dashedName

id	title	challengeType	dashedName
68b7cadffed0e75a517da673	Challenge 52: Binary to Decimal	29	challenge-52

--description--

Given a string representing a binary number, return its decimal equivalent as a number.

A binary number uses only the digits 0 and 1 to represent any number. To convert binary to decimal, multiply each digit by a power of 2 and add them together. Start by multiplying the rightmost digit by 2^0, the next digit to the left by 2^1, and so on. Once all digits have been multiplied by a power of 2, add the result together.

For example, the binary number 101 equals 5 in decimal because:

1 * 2^2 + 0 * 2^1 + 1 * 2^0 = 4 + 0 + 1 = 5

--hints--

to_decimal("101") should return 5.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(to_decimal("101"), 5)`)
}})

to_decimal("1010") should return 10.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(to_decimal("1010"), 10)`)
}})

to_decimal("10010") should return 18.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(to_decimal("10010"), 18)`)
}})

to_decimal("1010101") should return 85.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(to_decimal("1010101"), 85)`)
}})

--seed--

--seed-contents--

def to_decimal(binary):

    return binary

--solutions--

def to_decimal(binary):
    decimal = 0
    for i, bit_char in enumerate(reversed(binary)):
        bit = int(bit_char)
        decimal += bit * (2 ** i)
    return decimal