# Go deh!

Mainly Tech projects on Python and Electronic Design Automation.

## Sunday, May 27, 2012

### Python: Choice of the one obvious way to do it.

I just worked on a new Rosetta Code task on Fibonacci-like sequences where the solution works by giving the initial conditions and being returned something that can then create members of the defined series. You create a series generator factory then use the series generator returned. (The above uses the word generator in its non programming specific sense).

### Python: function returning a function

```>>> def fiblike(start):
memo = start[:]
def fibber(n):
try:
return memo[n]
except IndexError:
ans = sum(fibber(i) for i in range(n-addnum, n))
memo.append(ans)
return ans
return fibber

>>> fibo = fiblike([1,1])
>>> [fibo(i) for i in range(10)]
[1, 1, 2, 3, 5, 8, 13, 21, 34, 55]
>>> lucas = fiblike([2,1])
>>> [lucas(i) for i in range(10)]
[2, 1, 3, 4, 7, 11, 18, 29, 47, 76]
>>> for n, name in zip(range(2,11), 'fibo tribo tetra penta hexa hepta octo nona deca'.split()) :
fibber = fiblike([1] + [2**i for i in range(n-1)])
print('n=%2i, %5snacci -> %s ...' % (n, name, ' '.join(str(fibber(i)) for i in range(15))))

n= 2,  fibonacci -> 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 ...
n= 3, tribonacci -> 1 1 2 4 7 13 24 44 81 149 274 504 927 1705 3136 ...
n= 4, tetranacci -> 1 1 2 4 8 15 29 56 108 208 401 773 1490 2872 5536 ...
n= 5, pentanacci -> 1 1 2 4 8 16 31 61 120 236 464 912 1793 3525 6930 ...
n= 6,  hexanacci -> 1 1 2 4 8 16 32 63 125 248 492 976 1936 3840 7617 ...
n= 7, heptanacci -> 1 1 2 4 8 16 32 64 127 253 504 1004 2000 3984 7936 ...
n= 8,  octonacci -> 1 1 2 4 8 16 32 64 128 255 509 1016 2028 4048 8080 ...
n= 9,  nonanacci -> 1 1 2 4 8 16 32 64 128 256 511 1021 2040 4076 8144 ...
n=10,  decanacci -> 1 1 2 4 8 16 32 64 128 256 512 1023 2045 4088 8172 ...
>>> ```

### Python: Callable class

```>>> class Fiblike():
def __init__(self, start):
self.memo = start[:]
def __call__(self, n):
try:
return self.memo[n]
except IndexError:
ans = sum(self(i) for i in range(n-self.addnum, n))
self.memo.append(ans)
return ans

>>> fibo = Fiblike([1,1])
>>> [fibo(i) for i in range(10)]
[1, 1, 2, 3, 5, 8, 13, 21, 34, 55]
>>> lucas = Fiblike([2,1])
>>> [lucas(i) for i in range(10)]
[2, 1, 3, 4, 7, 11, 18, 29, 47, 76]
>>> for n, name in zip(range(2,11), 'fibo tribo tetra penta hexa hepta octo nona deca'.split()) :
fibber = Fiblike([1] + [2**i for i in range(n-1)])
print('n=%2i, %5snacci -> %s ...' % (n, name, ' '.join(str(fibber(i)) for i in range(15))))

n= 2,  fibonacci -> 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 ...
n= 3, tribonacci -> 1 1 2 4 7 13 24 44 81 149 274 504 927 1705 3136 ...
n= 4, tetranacci -> 1 1 2 4 8 15 29 56 108 208 401 773 1490 2872 5536 ...
n= 5, pentanacci -> 1 1 2 4 8 16 31 61 120 236 464 912 1793 3525 6930 ...
n= 6,  hexanacci -> 1 1 2 4 8 16 32 63 125 248 492 976 1936 3840 7617 ...
n= 7, heptanacci -> 1 1 2 4 8 16 32 64 127 253 504 1004 2000 3984 7936 ...
n= 8,  octonacci -> 1 1 2 4 8 16 32 64 128 255 509 1016 2028 4048 8080 ...
n= 9,  nonanacci -> 1 1 2 4 8 16 32 64 128 256 511 1021 2040 4076 8144 ...
n=10,  decanacci -> 1 1 2 4 8 16 32 64 128 256 512 1023 2045 4088 8172 ...
>>> ```

### Generator

```from itertools import islice, cycle

def fiblike(tail):
for x in tail:
yield x
for i in cycle(xrange(len(tail))):
tail[i] = x = sum(tail)
yield x

fibo = fiblike([1, 1])
print list(islice(fibo, 10))
lucas = fiblike([2, 1])
print list(islice(lucas, 10))

suffixes = "fibo tribo tetra penta hexa hepta octo nona deca"
for n, name in zip(xrange(2, 11), suffixes.split()):
fib = fiblike([1] + [2 ** i for i in xrange(n - 1)])
items = list(islice(fib, 15))
print "n=%2i, %5snacci -> %s ..." % (n, name, items)```
Output:
```[1, 1, 2, 3, 5, 8, 13, 21, 34, 55]
[2, 1, 3, 4, 7, 11, 18, 29, 47, 76]
n= 2,  fibonacci -> [1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610] ...
n= 3, tribonacci -> [1, 1, 2, 4, 7, 13, 24, 44, 81, 149, 274, 504, 927, 1705, 3136] ...
n= 4, tetranacci -> [1, 1, 2, 4, 8, 15, 29, 56, 108, 208, 401, 773, 1490, 2872, 5536] ...
n= 5, pentanacci -> [1, 1, 2, 4, 8, 16, 31, 61, 120, 236, 464, 912, 1793, 3525, 6930] ...
n= 6,  hexanacci -> [1, 1, 2, 4, 8, 16, 32, 63, 125, 248, 492, 976, 1936, 3840, 7617] ...
n= 7, heptanacci -> [1, 1, 2, 4, 8, 16, 32, 64, 127, 253, 504, 1004, 2000, 3984, 7936] ...
n= 8,  octonacci -> [1, 1, 2, 4, 8, 16, 32, 64, 128, 255, 509, 1016, 2028, 4048, 8080] ...
n= 9,  nonanacci -> [1, 1, 2, 4, 8, 16, 32, 64, 128, 256, 511, 1021, 2040, 4076, 8144] ...
n=10,  decanacci -> [1, 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1023, 2045, 4088, 8172] ...```

So how does the existence of three ways of giving an answer square with that part of the Zen of Python which states:
There should be one-- and preferably only one --obvious way to do it.

This comes down to a matter of style. Python supports many programming styles, (often called programming paradigms). What example might best fit a situation should depend on the surrounding programming style in use. The function calling a function, callable class, and generator solutions might best fit situations where it is to fit within programs using the procedural, object-oriented and functional styles respectively.

## Wednesday, May 02, 2012

### Could N'T care less

I was just enjoying the book "A rising thunder" by David Weber when I came across the phrase "I could care less" (page 448 of the BAEN hardback), meaning in its context: "I could not care less" i.e. there is no lesser degree of care that I could hold.

I would have thought that even though the phrase may be common usage in the U.S. an author would add the correct phrase. This just jars.