1. `demo.py`:支持迭代的类,正向迭代与反向迭代

2. `genitor.py`:生成器的类,用于迭代

3. `iterator_visit.py`:迭代器的访问:如`islice`访问生成器指定起始和终止点,跳过指定位置的元素,元素的排列组合,迭代添加索引,同时迭代多个序列,`zip`合并序列的访问,`chain`不同数据在一起迭代访问,将列表展平

class linehistory:

def __init__(self, lines, histlen=3):

self.lines = lines

self.history = deque(maxlen=histlen)

def __iter__(self):

# 索引从 1 开始

for lineno, line in enumerate(self.lines, 1):

self.history.append((lineno, line))

yield line

def clear(self):

self.history.clear()

yield lineno, line

with open('demo.py') as f:

with open('demo.py', encoding='utf-8') as f:

lines = linehistory(f)

for line in lines:

for lineno, hline in lines.history:

print('{}:{}'.format(lineno, hline), end='')

for lineno, line in lines:

print(lineno, ': ', line, end='')

# for lineno, hline in lines.history:

# print('{}:{}'.format(lineno, hline), end='')

f = open('demo.py')

f = open('demo.py', encoding='utf-8')

lines = linehistory(f)

t = iter(lines)

print(next(t))

with open('/etc/passwd') as f:

# 去掉文件头部的行

for line in dropwhile(lambda line: not line.startswith('#'), f):

# 如下的写法会去掉注释行

# lines = (line for line in f if not line.startswith('#'))

print(line, end='')

items = ['a', 'b', 'c', 1, 4, 10, 15]

items = ['a', 'b', 'c', 1, 2, 4, 10, 15]

for x in islice(items, 3, None):

print(x)

for p in permutations(items):

print(p)

print(p,)

print('--------')

for p in permutations(items, 2):

print(p)

print('--------')

for i in combinations(items, 2):

print(i)

print('--------')

for c in combinations_with_replacement(items, 3):

print(c)

print('--------')

items = [1, 2, [3, 4, [5, 6], 7], 8]

for x in flatten(items):

print(x)

# sep=':' 不行,只有一个输出

print(x, end=', ')

items = ['Dave', 'Paula', ['Thomas', 'Lewis']]

for x in flatten(items):

print(x)