### Question :

I’d simply like to convert a base-2 binary number string into an int, something like this:

```
>>> '11111111'.fromBinaryToInt()
255
```

Is there a way to do this in Python?

##
Answer #1:

You use the built-in `int`

function, and pass it the base of the input number, i.e. `2`

for a binary number:

```
>>> int('11111111', 2)
255
```

##
Answer #2:

Just type **0b11111111** in python interactive interface:

```
>>> 0b11111111
255
```

##
Answer #3:

Another way to do this is by using the `bitstring`

module:

```
>>> from bitstring import BitArray
>>> b = BitArray(bin='11111111')
>>> b.uint
255
```

Note that the unsigned integer is different from the signed integer:

```
>>> b.int
-1
```

The `bitstring`

module isn’t a requirement, but it has lots of performant methods for turning input into and from bits into other forms, as well as manipulating them.

##
Answer #4:

Using int with base is the right way to go. I used to do this before I found int takes base also. It is basically a reduce applied on a list comprehension of the primitive way of converting binary to decimal ( e.g. 110 = 2**0 * 0 + 2 ** 1 * 1 + 2 ** 2 * 1)

```
add = lambda x,y : x + y
reduce(add, [int(x) * 2 ** y for x, y in zip(list(binstr), range(len(binstr) - 1, -1, -1))])
```

##
Answer #5:

If you wanna know what is happening behind the scene, then here you go.

```
class Binary():
def __init__(self, binNumber):
self._binNumber = binNumber
self._binNumber = self._binNumber[::-1]
self._binNumber = list(self._binNumber)
self._x = [1]
self._count = 1
self._change = 2
self._amount = 0
print(self._ToNumber(self._binNumber))
def _ToNumber(self, number):
self._number = number
for i in range (1, len (self._number)):
self._total = self._count * self._change
self._count = self._total
self._x.append(self._count)
self._deep = zip(self._number, self._x)
for self._k, self._v in self._deep:
if self._k == '1':
self._amount += self._v
return self._amount
mo = Binary('101111110')
```

##
Answer #6:

A recursive Python implementation:

```
def int2bin(n):
return int2bin(n >> 1) + [n & 1] if n > 1 else [1]
```

##
Answer #7:

If you are using python3.6 or later you can use f-string to do the

conversion:

Binary to decimal:

```
>>> print(f'{0b1011010:#0}')
90
>>> bin_2_decimal = int(f'{0b1011010:#0}')
>>> bin_2_decimal
90
```

binary to octal hexa and etc.

```
>>> f'{0b1011010:#o}'
'0o132' # octal
>>> f'{0b1011010:#x}'
'0x5a' # hexadecimal
>>> f'{0b1011010:#0}'
'90' # decimal
```

Pay attention to 2 piece of information separated by colon.

In this way, you can convert between {binary, octal, hexadecimal, decimal} to {binary, octal, hexadecimal, decimal} by changing right side of colon[:]

```
:#b -> converts to binary
:#o -> converts to octal
:#x -> converts to hexadecimal
:#0 -> converts to decimal as above example
```

Try changing left side of colon to have octal/hexadecimal/decimal.

##
Answer #8:

For large matrix (10**5 rows and up) it is better to use a vectorized matmult. Pass in all rows and cols in one shot. It is extremely fast. There is no looping in python here. I originally designed it for converting many binary columns like 0/1 for like 10 different genre columns in MovieLens into a single integer for each example row.

```
def BitsToIntAFast(bits):
m,n = bits.shape
a = 2**np.arange(n)[::-1] # -1 reverses array of powers of 2 of same length as bits
return bits @ a
```