Python中迭代器与生成器怎么使用

x = 1.__iter__  # SyntaxError: invalid syntax

# 以下都是可迭代的对象
name = 'nick'.__iter__
print(type(name))  # 'method-wrapper'>

s = 'hello'
iter_s = s.__iter__()
print(type(iter_s))  # 'str_iterator'> iter_s为迭代器对象

while True:
    try:
        print(iter_s.__next__())
    except StopIteration:
        break
#hello

s = 'hello'
iter_s = iter(s) # 创建迭代器对象
print(type(iter_s))  #  iter_s为迭代器对象

while True:
    try:
        print(next(iter_s)) # 输出迭代器的下一个元素

    except StopIteration:
        break
# hello

#str
name = 'nick' 
for x in name:
    print(x)

#list
for x in [None, 3, 4.5, "foo", lambda: "moo", object, object()]:
    print("{0}  ({1})".fORMat(x, type(x)))

#dict
d = {
    '1': 'tasty',
    '2': 'the best',
    '3 sprouts': 'evil',
    '4': 'pretty Good'
}

for sKey in d:
    print("{0} are {1}".format(sKey, d[sKey]))

#file
f = open('32.txt', 'r', encoding='utf-8')
for x in f:
    print(x)
f.close()

class MyNumbers:
  def __iter__(self):
    self.a = 1
    return self
 
  def __next__(self):
    if self.a <= 20:
      x = self.a
      self.a += 1
      return x
    else:
      raise StopIteration
 
myclass = MyNumbers()
myiter = iter(myclass)
 
for x in myiter:
  print(x)

class Range:
    def __init__(self, n, stop, step):
        self.n = n
        self.stop = stop
        self.step = step

    def __next__(self):
        if self.n >= self.stop:
            raise StopIteration
        x = self.n
        self.n += self.step
        return x

    def __iter__(self):
        return self


for i in Range(1, 7, 3):
    print(i)

#1
#4

class Fib:
    def __init__(self):
        self._a = 0
        self._b = 1

    def __iter__(self):
        return self

    def __next__(self):
        self._a, self._b = self._b, self._a + self._b
        return self._a


f1 = Fib()
for i in f1:
    if i > 100:
        break
    print('%s ' % i, end='')

# 1 1 2 3 5 8 13 21 34 55 89

import sys


def fibonacci(n):  # 函数 - 斐波那契
    a, b, counter = 0, 1, 0
    while True:
        if counter > n:
            return
        yield a
        a, b = b, a + b
        counter += 1


f = fibonacci(10)  #f 是一个生成器
print(type(f))  # 'generator'>

while True:
    try:
        print(next(f), end=" ")
    except StopIteration:
        sys.exit()

def my_range(start, stop, step=1):
    while start < stop:
        yield start
        start += 1


g = my_range(0, 3)
print(f"list(g): {list(g)}")

def range(*args, **kwargs):
    if not kwargs:
        if len(args) == 1:
            count = 0
            while count < args[0]:
                yield count
                count += 1
        if len(args) == 2:
            start, stop = args
            while start < stop:
                yield start
                start += 1
        if len(args) == 3:
            start, stop, step = args
            while start < stop:
                yield start
                start += step

    else:
        step = 1

        if len(args) == 1:
            start = args[0]
        if len(args) == 2:
            start, stop = args

        for k, v in kwargs.items():
            if k not in ['start', 'step', 'stop']:
                raise ('参数名错误')

            if k == 'start':
                start = v
            elif k == 'stop':
                stop = v
            elif k == 'step':
                step = v

        while start < stop:
            yield start
            start += step


for i in range(3):
    print(i)  # 0,1,2

for i in range(99, 101):
    print(i)  # 99,100

for i in range(1, 10, 3):
    print(i)  # 1,4,7

for i in range(1, step=2, stop=5):
    print(i)  # 1,3

for i in range(1, 10, step=2):
    print(i)  # 1,3,5,7,9

t = (i for i in range(10))
print(t)  # <generator object  at 0x00000000026907B0>
print(next(t))  # 0
print(next(t))  # 1

with open('32.txt', 'r', encoding='utf8') as f:
    nums = [len(line) for line in f]  # 列表推导式相当于直接给你一筐蛋

print(max(nums))  # 2


with open('32.txt', 'r', encoding='utf8') as f:
    nums = (len(line) for line in f)  # 生成器表达式相当于给你一只老母鸡。

print(max(nums))  # ValueError: I/O operation on closed file.