Experimenting with For Loops (Python)

# a short look at some for loops and range() functions
# for loops iterate through sequences with iter() and generator objects with iter().next()
# tested with Python24     vegaseat    18sep2005

# range( [start,] stop[, step] ) creates a list of needed integer numbers, okay for short lists
# test increment, step = 2
print range(0, 10, 2)      # [0, 2, 4, 6, 8]

for k in range(0, 10, 2):
    print k
    
print

# test decrement, step = -1, count down from 10 to 1
print range(10, 0, -1)     # [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]

for k in range(10, 0, -1):
    print k

print
    
# xrange( [start,] stop[, step] ) function creates the integer number as needed, saves memory
#test
print xrange(0, 10, 2)        # xrange(0, 10, 2)
print list(xrange(0, 10, 2))  # [0, 2, 4, 6, 8]

for k in xrange(0, 10,2 ):
    print k

print

# qrange( [start,] stop[, step] ) is a generator, works similar to xrange()
def qrange(start, stop=None, step=1):
    """if start is missing it defaults to zero, somewhat tricky"""
    if stop == None:
        stop = start
        start = 0
    # allow for decrement
    if step < 0:
        while start > stop:
            yield start   # makes this a generator for new start value
            start += step
    else:
        while start < stop:
            yield start
            start += step

# test
print qrange(0, 10, 2)        # <generator object at 0x009D5E68>
print list(qrange(0, 10, 2))  # [0, 2, 4, 6, 8]

# for loop calls iter().next() to iterate through the generator object
for k in qrange(0, 10, 2):  # could use just qrange(10, 2), since start defaults to 0
    print k

print

# test decrement, count down from 10 to 1
for k in qrange(10, 0, -1):
    print k

print

# qrange() also takes floating point numbers, range() and xrange() do not!
for k in qrange(0, 1.0, 0.2):
    print k

print

# if you also want to show the index, use the new enumerate() function
for index, k in enumerate(range(0, 10, 2)):
    print "%d: %d" % (index, k)
    
print

# similar using qrange()
for index, k in enumerate(qrange(0, 1.0, 0.2)):
    print "%d: %0.1f" % (index, k)