parameters: (key, start, length)
return_statement: return reduce(lambda x,y: x*2+ord(y)-48, k, 0)
docstring: Extract a bitstring from a string of binary digits, and return its
      numeric value.
docstring_summary: Extract a bitstring from a string of binary digits, and return its
      numeric value.
docstring_tokens: Extract a bitstring from a string of binary digits and return its numeric value .
function: def _extract(key, start, length):
      """Extract a bitstring from a string of binary digits, and return its
      numeric value."""
      k=key[start:start+length]
      return reduce(lambda x,y: x*2+ord(y)-48, k, 0)
function_tokens: def _extract ( key , start , length ) : k = key [ start : start + length ] return reduce ( lambda x , y : x * 2 + ord ( y ) - 48 , k , 0 )