bin(num). convert ZERO and negative decimal numbers to binary.

conversions/decimal_to_binary.py

@@ -2,24 +2,57 @@
 
 
 def decimal_to_binary(num):
-    """Convert a Decimal Number to a Binary Number."""
+
+    """
+        Convert a Integer Decimal Number to a Binary Number as str.
+        >>> decimal_to_binary(0)
+        '0b0'
+        >>> decimal_to_binary(2)
+        '0b10'
+        >>> decimal_to_binary(7)
+        '0b111'
+        >>> decimal_to_binary(35)
+        '0b100011'
+        >>> # negatives work too
+        >>> decimal_to_binary(-2)
+        '-0b10'
+        >>> # other floats will error
+        >>> decimal_to_binary(16.16) # doctest: +ELLIPSIS
+        Traceback (most recent call last):
+        ...
+        TypeError: 'float' object cannot be interpreted as an integer
+        >>> # strings will error as well
+        >>> decimal_to_binary('0xfffff') # doctest: +ELLIPSIS
+        Traceback (most recent call last):
+        ...
+        TypeError: 'str' object cannot be interpreted as an integer
+    """
+
+    if type(num) == float:
+        raise TypeError("'float' object cannot be interpreted as an integer")
+    if type(num) == str:
+        raise TypeError("'str' object cannot be interpreted as an integer")
+
+    if num == 0:
+        return "0b0"
+
+    negative = False
+
+    if num < 0:
+        negative = True
+        num = -num
+
     binary = []
     while num > 0:
         binary.insert(0, num % 2)
         num >>= 1
-    return "".join(str(e) for e in binary)
 
+    if negative:
+        return "-0b" + "".join(str(e) for e in binary)
 
-def main():
-    """Print binary equivelents of decimal numbers."""
-    print("\n2 in binary is:")
-    print(decimal_to_binary(2))  # = 10
-    print("\n7 in binary is:")
-    print(decimal_to_binary(7))  # = 111
-    print("\n35 in binary is:")
-    print(decimal_to_binary(35))  # = 100011
-    print("\n")
+    return "0b" + "".join(str(e) for e in binary)
 
 
-if __name__ == '__main__':
-    main()
+if __name__ == "__main__":
+    import doctest
+    doctest.testmod()