Better looping, for string manipulation (python)
If i have this code
s = 'abcdefghi' for grp in (s[:3],s[3:6],s[6:]): print "'%s'"%(grp) total = calc_total(grp) if (grp==s[:3]): # more code than this p = total + random_value x1 = my_function(p) if (grp==s[3:6]): # more code than this p = total + x1 x2 = my_function(p) if (grp==s[6:]): # more code than this p = total + x2 x3 = my_function(p)
If the group is the first group, perform code for this group, if the group is the second group, perform code using the a value generated from code performed for the first group, the same applies for the third group, using a generated value from code for the second group:
How can i tidy this up to use better looping?
I'd code something like this as follows:
for i, grp in enumerate((s[:3],s[3:6],s[6:])): print "'%s'"%(grp) total = calc_total(grp) # more code that needs to happen every time if i == 0: # code that needs to happen only the first time elif i == 1: # code that needs to happen only the second time
etc. The == checks can be misleading if one of the groups "just happens" to be the same as another one, while the enumerate approach runs no such risk.
I may have misunderstood what you're doing, but it appears that you want to do something to s[:3] on the first iteration, something different to s[3:6] on the second, and something else again to s[6:] on the third. In other words, that isn't a loop at all! Just write those three blocks of code out one after another, with s[:3] and so on in place of grp.
I must say I agree with Peter in that the loop is redundant. If you are afraid of duplicating code, then just move the repeating code into a function and call it multiple times:
s = 'abcdefghi' def foo(grp): # Anything more you would like to happen over and over again print "'%s'"%(grp) return calc_total(grp) def bar(grp, value): total = foo(grp) # more code than this return my_function(total + value) x1 = bar(s[:3], random_value) x2 = bar(s[3:6], x1) x3 = bar(s[6:], x2)
# more code than this
contains non-duplicate code, then you must of course move that out of "bar" (which together with "foo" should be given a more descriptive name).
x = reduce(lambda x, grp: my_function(calc_total(list(grp)) + x), map(None, *[iter(s)] * 3), random_value)
At the end, you'll have the last x.
Or, if you want to keep the intermediary results around,
x =  for grp in map(None, *[iter(s)] * 3): x.append(my_function(calc_total(list(grp)) + (x or [random_value])[-1]))
Then you have x, x, x.
Get your data into the list you want, then try the following:
output = 0 seed = get_random_number() for group in input_list: total = get_total(group) p = total + seed seed = my_function(p)
input_list will need to look like ['abc', 'def', 'ghi']. But if you want to extend it to ['abc','def','ghi','jkl','mno','pqr'], this should still work.