On Wed, Jul 21, 2010 at 12:02 PM, Jack Diederich <jackdied@gmail.com> wrote:
2a) No control flow statements in the block means if you need to
augment the code to do a return/break/continue/yield you then have to
refactor so everything in the "given:" block gets moved to the top and
a 1-line change becomes a 10 line diff.
2b) Allowing control flow statements in the block would be even more confusing.
2c) Is this legal?
    x = b given:
      b = 0
      for item in range(100):
        b += item
        if b > 10:

2a) you are missing the point of the given clause. you use it to assign values to variables if, and only if, the only possible results of the computation are 
1) an exception is raised or
2) a value is returned which is set to the variable and used in the expression no matter its value.
if there is the slightest chance that what you describe might be necessary you would not put it in a "given" but do something like this: (assumes that a given is applied to the previous statement in its current block)

if some_bool_func(a):
    ans = some_func1(a, b, c)
    ans = some_func2(a, b, c)
given: # note: given applied to the block starting with the "if" statement
    a = get_a()
    b = get_b()
    c = get_c()

2b) agreed but there is no reason for them to be disallowed except readibility but they should be discouraged 
2c) see it might be okay, depending on what people think of your second question. in my opinion it should be illegal stylistically and be required to be changed to 

def summation(start, end)
    i = start
    while i < end:
        start += i
        i  += 1
    return start

def a_func():
    # do stuff
    x = b given:
        b = summation(0, 100)