[Tutor] Bit Strings

[Thomi Richards]

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Hi,

>
> Any suggestions?
>

I may have an idea ;)

essentially, what your code does is a binary count from 0 to 2^n (where n is 
the number of iterations / bits). right?

here's a sampel run of your code: (using 3 bits / iterations):

>>> bitStrings = []
>>> for a0 in [0,1]:
...     for a1 in  [0,1]:
...         for a2 in [0,1]:
...             oneString = str(a0)+str(a1)+str(a2)
...             bitStrings.append(oneString)
...                
>>> bitStrings
['000', '001', '010', '011', '100', '101', '110', '111']


Unless I'm mistaken, couldn't you do something like this:

>>> def bitStrings(iterations=3):
...     binary_strlist = []
...     for num in range(2**iterations):
...             binary_strlist.append(binary(num))
...     return binary_strlist
... 


which leaves us with the task of coding a decimal to binary converter. This is 
actually quite simple...One way to do it is to use a dictionary to convert 
from a hex value to a binary one (AFAIK, python doesn't have a binary 
converter. It does however have a hex converter). 

However, there are a couple of complications in this function:

1.- we could/should? pad the binary values with zero's.. so binary 1 becomes 
001, or 00000001 (for an 8 bit number)

2.- we can't do a direct map from decimal->hex-> binary, because we might be 
given a decimal larger than 15, which will result in a two digit hex 
number...

So, something like this:
>>> def binary(decimal):
...     bin_string = ''
...     map_dict = {
...     '0' : '0000',
...     '1' : '0001',
...     '2' : '0010',
...     '3' : '0011',
...     '4' : '0100',
...     '5' : '0101',
...     '6' : '0110',
...     '7' : '0111',
...     '8' : '1000',
...     '9' : '1001',
...     'a' : '1010',
...     'b' : '1011',
...     'c' : '1100',
...     'd' : '1101',
...     'e' : '1110',
...     'f' : '1111' }
...     for hexdigit in hex(decimal)[2:]:       #ignore the leading '0x'
...             bin_string += map_dict[hexdigit]
...     return bin_string

to test our decimal -> binary converter:
>>> binary(5)
'0101'
>>> binary(50)
'00110010'

Now we can test the whole thing:

bitStrings()

(this uses the default, 3 places)

for more places:
>>> bitStrings(5)
['0000', '0001', '0010', '0011', '0100', '0101', '0110', '0111', '1000', 
'1001', '1010', '1011', '1100', '1101', '1110', '1111', '00010000', 
'00010001', '00010010', '00010011', '00010100', '00010101', '00010110', 
'00010111', '00011000', '00011001', '00011010', '00011011', '00011100', 
'00011101', '00011110', '00011111']

As you can see, there's still some problems here.

I've been doing this all in the interactive window, and it's getting a bit 
cumbersome. Perhaps it's time for someone else to continue this ;P

It's pretty much there, and it's prettyextendable as well. (I would appreciate 
some feedback on this from some of the more experienced tutor list members as 
well ;)

anyway, i hope this helps!

Thanks,

- -- 
Thomi Richards,
http://once.sourceforge.net/


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