I have a byte (from some other vendor) where the potential bit masks are as follows:
value1 = 0x01 value2 = 0x02 value3 = 0x03 value4 = 0x04 value5 = 0x05 value6 = 0x06 value7 = 0x40 value8 = 0x80
I can count on ONE of value1 through value6 being present. And then value7 may or may not be set. value8 may or may not be set.
So this is legal: value2 | value7 | value8 This is not legal: value1 | value3 | value7
I need to figure out whether value 7 is set, value8 is set, and what the remaining value is.
I have the following python code. Is there a more elegant way to do this?
value1 = 0x01 value2 = 0x02 value3 = 0x03 value4 = 0x04 value5 = 0x05 value6 = 0x06 value7 = 0x40 value8 = 0x80 def format_byte_as_bits(value): return format(value,'b').zfill(8) def mask_bits_on_byte(byte,mask): inverse_of_mask = mask ^ 0b11111111 return byte & inverse_of_mask def parse_byte(byte): value7_set = byte & value7 == value7 value8_set = byte & value8 == value8 byte = mask_bits_on_byte(byte,value7) byte = mask_bits_on_byte(byte,value8) base_value = byte return value7_set,value8_set,base_value # Example 1 byte = value3 | value7 value7_set,value8_set,base_value = parse_byte(byte) print("base_value = "+str(base_value)) print("value7_set = "+str(value7_set)) print("value8_set = "+str(value8_set)) print() # Output: # base_value = 3 # value7_set = True # value8_set = False # Example 2 byte = value5 value7_set,value8_set,base_value = parse_byte(byte) print("base_value = "+str(base_value)) print("value7_set = "+str(value7_set)) print("value8_set = "+str(value8_set)) print() # Output: # base_value = 5 # value7_set = False # value8_set = False # Example 3 byte = value1 | value7 | value8 value7_set,value8_set,base_value = parse_byte(byte) print("base_value = "+str(base_value)) print("value7_set = "+str(value7_set)) print("value8_set = "+str(value8_set)) # Output: # base_value = 1 # value7_set = True # value8_set = True EDIT - I LOVE stackoverflow. So many useful answers, so quickly! You guys are awesome! Wish I could mark all the answers. But I'll at least give everyone an up vote!
EDIT2 - Based on the answers below, the code is simplified to the following:
value1 = 0x01 value2 = 0x02 value3 = 0x03 value4 = 0x04 value5 = 0x05 value6 = 0x06 value7 = 0x40 value8 = 0x80 def parse_byte(byte): return byte & value7, byte & 0x80, byte & 7 # Example 1 byte = value3 | value7 value7_set,value8_set,base_value = parse_byte(byte) print("base_value = "+str(base_value)) if value7_set: print("value7_set") if value8_set: print("value8_set") print() # Example 2 byte = value5 value7_set,value8_set,base_value = parse_byte(byte) print("base_value = "+str(base_value)) if value7_set: print("value7_set") if value8_set: print("value8_set") print() # Example 3 byte = value1 | value7 | value8 value7_set,value8_set,base_value = parse_byte(byte) print("base_value = "+str(base_value)) if value7_set: print("value7_set") if value8_set: print("value8_set") print() 4 Answers
Most of your value* constants aren't actually bit masks, only value7 and value8 are. I'd define another bit mask to extract the lower bits, so I would have three bit masks in total:
mask0 = 0x07 mask1 = 0x40 mask2 = 0x80 Now your function becomes
def parse_byte(byte): return byte & mask2, byte & mask1, byte & mask0 I did not convert the results to bool -- I don't see why this should be necessary. When checking the returned value with if, it will be implicitly converted to bool anyway.
Also note that
format(value,'b').zfill(8) can be simplified to
format(value,'08b') Given a value such as:
>>> x = 0b10001000 You can find out whether the top bits are set with:
>>> bit8 = bool(x & 0b10000000) >>> bit7 = bool(x & 0b01000000) To find which lower bit is set, use a dictionary:
>>> bdict = dict((1<<i, i+1) for i in range(6)) >>> bdict[x & 0b00111111] 4 You don't need the other two functions:
def parse_byte(byte): value7_set = byte & value7 == value7 value8_set = byte & value8 == value8 base_value = byte & 7 return value7_set,value8_set,base_value It's a little verbose but perfectly fine. The only change I'd make is to simplify parse_byte:
def parse_byte(byte): value7_set = byte & value7 == value7 value8_set = byte & value8 == value8 base_value = mask_bits_on_byte(byte,value7 | value8) return value7_set,value8_set,base_value 
