How to convert a binary (string) into a float value?

In one of your comments you indicated that the binary number represents a float in 8 byte long IEEE 754 binary64 format. However that is inconsistent with the -0b1110 value you showed as an example, so I've ignored it and used my own which is in the proper format as example input data for testing the answer shown below.

Essentially what is done is first the binary string is converted into an integer value, then next into a string of raw bytes which is passed to struct.unpack() for final conversion to a floating point value. The bin_to_float() function shown below drives the process. Although not illustrated, binary input string arguments can be prefixed with '0b'.

from codecs import decode
import struct


def bin_to_float(b):
    """ Convert binary string to a float. """
    bf = int_to_bytes(int(b, 2), 8)  # 8 bytes needed for IEEE 754 binary64.
    return struct.unpack('>d', bf)[0]


def int_to_bytes(n, length):  # Helper function
    """ Int/long to byte string.

        Python 3.2+ has a built-in int.to_bytes() method that could be used
        instead, but the following works in earlier versions including 2.x.
    """
    return decode('%%0%dx' % (length << 1) % n, 'hex')[-length:]


def float_to_bin(value):  # For testing.
    """ Convert float to 64-bit binary string. """
    [d] = struct.unpack(">Q", struct.pack(">d", value))
    return '{:064b}'.format(d)


if __name__ == '__main__':

    for f in 0.0, 1.0, -14.0, 12.546, 3.141593:
        print('Test value: %f' % f)
        binary = float_to_bin(f)
        print(' float_to_bin: %r' % binary)
        floating_point = bin_to_float(binary)  # Round trip.
        print(' bin_to_float: %f\n' % floating_point)

Output:

Test value: 0.000000
 float_to_bin: '0000000000000000000000000000000000000000000000000000000000000000'
 bin_to_float: 0.000000

Test value: 1.000000
 float_to_bin: '0011111111110000000000000000000000000000000000000000000000000000'
 bin_to_float: 1.000000

Test value: -14.000000
 float_to_bin: '1100000000101100000000000000000000000000000000000000000000000000'
 bin_to_float: -14.000000

Test value: 12.546000
 float_to_bin: '0100000000101001000101111000110101001111110111110011101101100100'
 bin_to_float: 12.546000

Test value: 3.141593
 float_to_bin: '0100000000001001001000011111101110000010110000101011110101111111'
 bin_to_float: 3.141593

This works for me. Tested with Python3.4:

def float_to_bin(num):
    return bin(struct.unpack('!I', struct.pack('!f', num))[0])[2:].zfill(32)

def bin_to_float(binary):
    return struct.unpack('!f',struct.pack('!I', int(binary, 2)))[0]

float_to_bin(bin_to_float(float_to_bin(123.123))) == float_to_bin(123.123)
>>> True