Converting binary to decimal integer output

Question

I need to convert a binary input into a decimal integer. I know how to go from a decimal to a binary:

n = int(raw_input('enter a number: '))
print '{0:b}'.format(n)

I need to go in the reverse direction. My professor said that when he checks our code, he is going to input 11001, and he should get 25 back. I've looked through our notes, and I cannot figure out how to do this. Google and other internet resources haven't been much help either.

The biggest problem is that we are not allowed to use built-in functions. I understand why we are not allowed to use them, but it's making this problem much more difficult, since I know Python has a built-in function for binary to decimal.

Solution 1

Binary to Decimal

int(binaryString, 2)

Decimal to Binary

format(decimal ,"b")

Solution 2

There is actually a much faster alternative to convert binary numbers to decimal, based on artificial intelligence (linear regression) model:

1. Train an AI algorithm to convert 32-binary number to decimal based.
2. Predict a decimal representation from 32-binary.

See example and time comparison below:

from sklearn.linear_model import LinearRegression
from sklearn.model_selection import train_test_split
import numpy as np

y = np.random.randint(0, 2**32, size=10_000)

def gen_x(y):
    _x = bin(y)[2:]
    n = 32 - len(_x)
    return [int(sym) for sym in '0'*n + _x]

X = np.array([gen_x(x) for x in y])

model = LinearRegression()
model.fit(X, y)

def convert_bin_to_dec_ai(array):
    return model.predict(array)

y_pred = convert_bin_to_dec_ai(X)

Time comparison:

This AI solution converts numbers almost x10 times faster than conventional way!

Solution 3

If you want/need to do it without int:

sum(int(c) * (2 ** i) for i, c in enumerate(s[::-1]))

This reverses the string (s[::-1]), gets each character c and its index i (for i, c in enumerate(), multiplies the integer of the character (int(c)) by two to the power of the index (2 ** i) then adds them all together (sum()).