在Python中创建一个"实际"for循环？

Question

正如您应该知道的,在Python中,以下是Python中有效的for循环:

animals = [ 'dog', 'cat', 'horse' ] # Could also be a dictionary, tuple, etc

for animal in animals:
    print animal + " is an animal!"

这通常很好.但在我的情况下,我想像在C/C++/Java等中那样创建一个for循环.for循环看起来像这样:

for (int x = 0; x <= 10; x++) {
    print x
}

我怎么能在Python中做这样的事情？我是否必须设置这样的东西,或者是否有一种实际的方法可以做到这一点我缺少(我已经用Google搜索了好几周):

i = 0

while i is not 10:
    print i

或者有一个如何做到这一点的标准？我发现以上并不总是有效.是的,对于上述情况,我可以这样做:

for i in range(10):
    print i

但就我而言,我不能这样做.

Answer 1

为什么需要C风格的索引跟踪循环？我可以想象一些案例.

# Printing an index
for index, name in enumerate(['cat', 'dog', 'horse']):
  print "Animal #%d is %s" % (index, name)

# Accessing things by index for some reason
animals = ['cat', 'dog', 'horse']
for index in range(len(animals)):
  previous = "Nothing" if index == 0 else animals[index - 1]
  print "%s goes before %s" % (previous, animals[index])

# Filtering by index for some contrived reason
for index, name in enumerate(['cat', 'dog', 'horse']):
  if index == 13:
    print "I am not telling you about the unlucky animal"
    continue  # see, just like C
  print "Animal #%d is %s" % (index, name)

如果你真的很想模仿一个反跟踪循环,你就有了图灵完备的语言,这可以做到:

# ...but why?
counter = 0
while counter < upper_bound:
  # do stuff
  counter += 1

如果您觉得有必要重新分配循环计数器变量中间循环,那么你做错了很可能很高,无论是C循环还是Python循环.

Answer 2

我猜从你的评论中你试图循环网格索引.以下是一些方法:

简单的双循环:

for i in xrange(width):
    for j in xrange(height):
         blah

使用itertools.product

for i, j in itertools.product(xrange(width), xrange(height)):
     blah

如果可以,使用numpy

x, y = numpy.meshgrid(width, height)
for i, j in itertools.izip(x.reshape(width * height), y.reshape(width * height):
    blah