How to define and use Python generators appropriately

Question

I want to define a generator from a list that will output the elements one at a time, then use this generator object in an appropriate manner.

a = ["Hello", "world", "!"]
b = (x for x in a)
c = next(b, None)
while c != None:
    print c,
    c = next(b, None)

Is there anything wrong or improvable with the while approach here? Is there a way to avoid having to assign 'c' before the loop?

Thanks!

Answer 1

Why would you use a while loop? In Python, for loops are absolutely designed for this:

a = ["Hello", "world", "!"]
b = (x for x in a)
for c in b:
    print c,

If you are stuck on a while implementation for whatever reason, your current implementation is probably the best you can do, but it's a bit clunky, don't you think?

Answer 2

Clarification: you meant generator expressions not generators -- the latter is a function definition that contains at least one yield statement/expression.

agreed with the earlier poster... you should be using for loops for almost everything. i rarely use while loops, which are relegated to simple counters or servers running infinite loops. :-)

you can also put the genexp on the same line as the for loop...

a = ["Hello", "world", "!"]
for c in (x for x in a):
    print c,

...since the genexp can't be reused. however, it doesn't look as readable. also, this defeats the purpose of this exercise. why not just iterate over a itself?

for c in ["Hello", "world", "!"]:
    print c,

you've already used up memory to make the list; why create a genexp when it's not nec?